Combining semi-structured and integrative reviews of literature on resistance in art and aesthetics across the humanities and social sciences, the paper performs a thematic analysis to identify patterns in AR’s definitions, modes and domains, attributes, and transformative variables. These are synthesized in terms of the evolving resistance studies’ frameworks and an understanding of aesthetics as relating to the sensorium, ultimately revealing three interlocking issues: (1) publicness, (2) potentiality, and (3) plexus. These AR-specific issues contribute to the categorization of resistance, its identification, and the tracing of its network en route to change.This paper explicates the concept of  The long history of, and frequent allusion to, aesthetic resistance emphasizes the specificity and significance of the term, and the need to understand it within the frameworks of resistance studies. Inconsistencies in the use of this notion across fields hinder its discussion, theorization, and development, however—not least in its connection to resistance studies. This paper therefore seeks to bridge interdisciplinary gaps by analyzing literature on resistance in art and aesthetics from a broad range of fields in the humanities and social sciences. In essence, this literature discusses aesthetic resistance—henceforth referred to as AR. In the coming analysis I establish AR as an umbrella concept wherein aesthetics is understood through the lens of the sensorium, a perspective I will clarify in a later section. After exploring various definitions of AR used across the literature, I delineate the concept by way of three thematic categories: AR’s (1) modes and domains, (2) attributes, and (3) transformative variables. I then collate these categories with resistance studies’ rapidly evolving analytical frameworks in order to identify avenues for future research. These avenues address three intertwining issues—(1) AR’s continuum of publicness, (2) its focus on potentiality in place of intention, and (3) its positions in the plexus of sociopolitical change—which together are key to understanding resistance as a whole: its categorization, its identification, and its connection to sociopolitical change.What is Examining aesthetics and politics, philosopher Jacques Rancière ascribes the lexical homonymy of the term ‘resistance’ to art’s presumed capacity to resist various forms of power. AR against power is susceptible to conflation with the material resistance that is inherent in the process of making artworks, and with the product that resists the passage of time  to find relevant sections to close-read from within the larger body of the articles. I continuously recategorized my thematic nodes during this manual coding. The resulting patterns, then, were derived from recategorizing these thematic nodes in my NVivo codebook.et al.The analysis benefits from prior resistance research like Hollander and Einwohner , RESIST’3.etal.In the humanities, the term ‘resistance’ has been frequently used for nearly a century. Numerous scholars and practitioners have employed the term in a manner similar to how painters apply a primer for their canvas: as a foundational layer onto which they affix meanings, forms, and implications  domains and modes, (2) attributes, and (3) transformative variables. These theme categories, as I will discuss after this section, spurred my proposed AR key issues: its publicness, its potentiality, and its plexus.How is resistance in art and aesthetics perceived and discussed across these adjacent disciplines? How do these perceptions and discussions relate to sociopolitical transformation? In this section, I will describe several theme categories that became apparent in this vast body of AR literature, starting with 3.1.Art as Experience  since the parasite’s relationship with the host considers a dependency where there is ‘no outside.’ For Fisher, a parasite, moreover, will never terminate its host, for the sake of maintaining its own life (Anna Watkins Fisher then brought the concept of the parasite into the artistic resistance discourse 2020). Drawing from Michel Serres’s work, James Scott’s the weak , and emb. DrawingSchlußakkord (1936) and discussing two others also produced by the UFA during the Third Reich, scholar of German Studies Linda Schulte-Sasse doubts the ‘glamour’ that the term ‘resistance’ implies, and opts instead for a ‘reflexive space’  as a case study, cultural study theorists Anne Ring Petersen and Sabine Dahl Nielsen propose the concept of ‘postmigrant public spaces’—‘plural and sometimes conflictual arenas of human encounter shaped by immigration, nationalism and social inequity’ (Trade/Trace/Transit (2014–16), which traces the complex social aesthetics along an informal trade route of the cardboard waste trade in Hong Kong, offers ‘a platform for counter narratives in the public sphere’ , which took place between 1990 and 1993, a twenty-year retrospective of the Chicano Civil Rights Movement touring more than 140 artworks by more than 90 Chicano/a artists in public museums across ten US cities. Chicana writer/scholar/activist Alicia Gaspar de Alba argues that CARA’s most significant contribution lies in ‘its resistance to traditional museum and market practices, its complex organizational structure, its politics of self-representation, and its reception by the different communities that it addressed and/or confronted’  is uniquely placed. Born out of the then newly elected Chilean president Salvador Allende’s counter-information campaign as a defense from media attacks, it is a ‘museum against museum, an anti-museum,’ openly denouncing the segregating art system that degrades art and artists, as sociologist and curator María Berríos argues  after only 4 short days. Millions of people from around the world saw these events depicted in newspaper and on television and, not surprisingly, reproductions of the Tiananmen Square monument soon began emerging in public spaces around the globe , p. 314.‘To whom must a resistant work communicate its resistance?’ asks Schulte-Sasse in her discussion of Sirk’s reflexive space , p. 3. T Führer’ , p. 29. ’ et al. . We find’ et al. . Darts petal.’s analytical point regarding how ‘power and resistance exist in a mutually constitutive relationship’  and modes (the use of a monument as a reproducible object) with the attributes of AR: disruption, visibility, circulation, duration.Darts’s description not only demonstrates Baaz ionship’ , p. 145.The Uruguayan Tupamaros pushes circulation into culture a step further. Their strategy papers included what they called an ‘armed propaganda’ . Awareness of this valuation bias seems already pervasive: socially engaged art awarding institutions such as the Vera List Centre on Art and Politics , for exa, p. 131.et al. etal. discuss—would be very difficult to see or prove  the conflation of aesthetics and art furthered by the distinction between art and everyday life, (2) the privileging of the visual over other senses, and of visual representations over other forms of aesthetics, and (3) the limiting of aesthetics as beauty. Contestations to these challenges include debates and evidence from neuroaesthetics as an emerging field, evolutionary biology, psychology, and occupational science. Firstly, aesthetic processing is not only ‘a general cognitive process that applies to both non-art and art objects’ but also—secondly—frequently involves multi-modal sensations other than vision  mirror—one of the most long-standing and widespread notions appearing in approximately 56% of my initial sample literature—onto what aesthetics activates: what is reflected, how it is reflected, what it is, and how it is perceived. This, accordingly, provides a broader frame of reference to understand the continuum between actors at different nodes of AR. The lens of the sensory makes it possible to analyze the potentiality of the varying forms I described previously in a continuum of publicness—from Barnes’s uncoordinated, individually enacted, vocal aesthetic resistance . How can we reconcile possibilities of resistance within a totalitarian system—a system with ‘no outside’—that absorbs everything into its desire  more constructive in terms of duration, as it enables post-event and posthumous debates, like in the cases of CARA and Sirk as discussed earlier. Johansson and Vinthagen even went as far as eliminating the subject from their analysis of resistance practice to focus on the act itself, as Lilja discusses , p. 206,4.4.Adopting another term from biology, we can think of the network of transformative variables in terms of a ‘plexus.’ This neuroanatomical term may support an imaginary of transformative variables as an interconnected living system. It goes hand in hand with the broader mind map as a reminder of the publicness continuum, and enduring potentiality in the impossibility of downright revolution. Like plexuses of nerves, for example, AR may serve both functions of the sensory and the motor—imagination, emotions, and mobilization—in society.One pattern specific to AR, as discussed earlier, is the notion that AR does not directly alter socio-political institutions. Chenoweth  observesIn his polemic with Rasmussen, Kester argues for an evolution through capillary action. Thinking of Fisher’s parasitical resistance encourages me to imagine a parasite-host co-evolution, where parasites can mediate evolutionary social behavior in hosts. This evolutionary pace makes sense, especially considering the temporal requirement of cultural transformation, one of AR’s domains. We have seen examples where AR projects continue to be discussed post-event for decades. Other nonhuman actors like physical objects also embark on similar durational journeys, which can span anywhere along the continuum from public space  to intimate space . Longitudinally tracing these physical objects in connection to the larger sociopolitical change undoubtedly requires appropriate methodologies. It does, however, represent a promising direction for empirical AR research, which may contribute to understanding the mechanism of resistance.5.I have attempted to explicate AR—short for ‘aesthetic resistance’—and elucidate its connection to sociopolitical transformation, by way of reviewing literature across fields. The significantly sized study is by no means exhaustive, precisely because of its broad nature and limited space for discussion. The sampling, analysis, and synthesis of the literature may still be influenced by my personal bias as an artist and practice-based researcher. I am implicated in a search for meaningful resistance, even if such an ideal may never be achieved because of the subject’s complexity. The study’s language limitation also implies a lack of samples from cultures where aesthetics and resistance may be thought of differently—although I personally hail from and have one foot in such culture, which means I may in turn have my own biases. I have detailed my attempt to methodically mitigate these biases early in this paper.Methodologically, I combined semi-structured with integrative review, and through an inductive thematic analysis I have discussed patterns in AR’s definitions, modes and domains, attributes, and transformative variables. Synthesizing these within the rapidly evolving framework of resistance studies, I thereby reconceptualized aesthetics in AR in terms of the sensory: aesthetics as an embodied tool to stimulate imagination and emotions, that is neither limited to art, nor to the visual, nor to beauty. This allowed me to argue for three intertwining challenges for AR: to (1) rethink its categorization in terms of continuum of publicness, (2) propose an identification angle of potentiality instead of intent, and (3) trace how it connects to sociopolitical changes through looking at its vehicular positions in the plexus of transformative variables. This, I propose, contributes to the contemporary framework of resistance studies—as the very framework that enabled its analysis—in two ways: not only has AR never been previously theorized despite being alluded to across fields for almost a century, these three key issues can also provoke similar questions to comprehend resistance in general.


The rich literature in phenomenological psychopathology regards the communicative difficulties accompanying psychiatric illness as a product of ‘unworlding‘: the experience of a drastic change in one’s habitual field of experience. This paper argues that the relationship between speech expression and unworlding in psychiatric illness is more complex than previously assumed. Not only does unworlding cause a breakdown in speech expression, but a breakdown in speech expression can perpetuate, and even exacerbate, the experience of unworlding characteristic of psychiatric illness. In other words, I identify a two-way relationship between unworlding and the communication breakdown in psychiatric illness. Merleau-Ponty’s phenomenology of speech expression is drawn upon to demonstrate how hermeneutical injustice in psychiatric healthcare can elicit unworlding for the person with a psychiatric illness. There is a long tradition of employing a phenomenological approach to gain greater insight into the unique experience of psychiatric illness. Researchers in this field have shed light upon a disturbance in the overall structure of experience characteristic of psychiatric illness, which causes the embodied subject to encounter the world in a fundamentally different way from their neuro-normative counterparts. This disturbance can be referred to as “unworlding”, a term popularized by Louis Sass  but deriThe paper aims to better understand the relationship between “unworlding” and ineffability in psychiatric illness. Drawing on Merleau-Ponty’s phenomenology of speech expression, I argue that “unworlding” not only causes a breakdown in speech expression but a breakdown in speech expression can perpetuate, and even exacerbate, the experience of “unworlding” characteristic of psychiatric illness. In other words, I identify a two-way relationship between “unworlding” and the communication breakdown in psychiatric illness.This paper begins with a brief account of “unworlding” and its application in phenomenological psychopathology. It then illuminates the unequal hermeneutical landscape in psychiatric healthcare that drives inexpressibility. I identify this as hermeneutical injustice. The final two sections consider how hermeneutical injustice can constitute a breakdown in the body schema for the person with psychiatric illness due to the deprivation of an essential bodily capacity: speech expression. Thus, I demonstrate how hermeneutical injustice can give rise to “unworlding” in psychiatric illness.synthesis. The concept of “being-in-the-world” was first introduced by Heidegger to denote the cohesive whole of a subject and their environment. In addition, feeling at home in the world also consists of cohesion in one’s body, time and space. According to Heidegger, the subject (Dasein) does not merely “inhabit” the world, like a person positioned in a space, but “dwells” in the world, like a person belonging to a home and experiencing a “simple oneness” with their surroundings: “ich bin, du bist means: I dwell, you dwell. The way in which you are and I am, the manner in which we humans are on the earth, is Bauen, dwelling” . The example of unworlding that Heidegger provides is that of Dasein’s existence during an era of war: “the ‘world’ has become an unworld as a consequence of the abandonment of beings by Being’s truth” ; while for the person outside the sufferer’s body, what is effortless is not grasping it” Scarry, , p. 4.4  Styron, , p. 5. SScholars in the phenomenology of illness have attributed this communication breakdown to the fundamental taken-for-granted elements of the world being drastically altered for the person with a psychiatric illness. Due to a monumental shift in the ill person’s embodied experience, she is thrust into an unfamiliar life-world with new, confusing, and inexpressible meaning-structures. As such, people with psychiatric illness become “experientially unmoored from the lived spaces of their everyday environments” Krueger, , p. 602.Sometimes, this difficulty is no doubt partly attributable to effects that depression has on one’s cognitive abilities. But people still struggle to convey the experience after recovering, and their accounts often suggest that the problem stems from its very nature. Depression involves a disturbance of something that is fundamental to our lives, something that goes unnoticed when intact. What is eroded or lost is a “sense” or “feeling” of being comfortably immersed in the world. a language requires a “taking up of the world”, a dwelling in the environment. Language is the core structure of our being-in-the-world. It is a form of bodily comportment that discloses the meaning of the world and is, therefore, central to our ability to move through our environment with a pre-reflective openness. For this reason, the meaning of one language can never be fully translatable to the meaning of another as this would require existing in two different worlds simultaneously dwell in more than one world. Like the duck-rabbit illusion made famous by Wittgenstein (where one can never see the duck and rabbit simultaneously), a person can only be immersed in one linguistic world at a time  begins with an exploration of the phenomenology of language. Like Merleau-Ponty, Fanon recognized that “To speak means being able to use a certain syntax and possessing the morphology of such and such a language, but it means above all assuming a culture and bearing the weight of a civilization”  speaking Antillean who moves to France and attempts to assimilate the “proper” French language. He does so, according to Fanon, because “proper” French is (mistakenly) regarded as the golden ticket that grants permission to a white world: “the more the black Antillean assimilates the French language, the whiter he gets- i.e., the closer he comes to becoming a true human being” Fanon, , p. 2. C” Fanon, , p. 20. Fanon helps us expose a gap in Merleau-Ponty’s phenomenology of speech expression as this phenomenological account is limited to those granted a hermeneutical privilege. Only those in a dominant social position have the status as “speaking subject”, and the subject-world synthesis that accompanies it. Fanon limits his analogy to all persons who are colonized. Still, it would not be a stretch to argue that other features of one’s embodiment  has the power to inhibit one’s membership to the community of speaking subjects.What Fanon identifies can be termed “Epistemic injustice”. Epistemic injustice was first theorized by Fricker to “delineate a distinctive class of wrongs, namely those in which someone is disingenuously downgraded and/or disadvantaged in respect of their status as an epistemic subject” Fricker, , p. 53. To exemplify hermeneutical injustice, Fricker presents the case of victims of sexual harassment prior to the 1960s. Because certain groups most likely to be targeted by sexual harassers were excluded from the construction of interpretive frameworks in the workplace, experiences of sexual harassment were not part of the collective understanding. Instead, “repeated sexual propositions in the workplace [were] never anything more than a form of “flirting”, and their uneasy rejection by the recipient only ever a matter of her lacking a ‘sense of humor”  as being more or less depleted . Only the hermeneutically privileged can contribute toward, alter, and remove resources from the pool of shared ideas. The hermeneutically marginalized do not have this power and are forced to contend with ill-fitting concepts.The cognitive disablement prevents her from understanding a significant patch of her own experience: that is, a patch of experience which it is strongly in her interests to understand, for without that understanding she is left deeply troubled, confused, and isolated, not to mention vulnerable to continued harassmentFricker, , p. 151. Fricker understands hermeneutical resources as essential for meaning-making; where hermeneutical resources are missing from the interpretive framework, the subject’s grasp of their experience is distorted, limited, or otherwise confined.Two harms emerge from hermeneutical injustice. The first is an epistemic harm, whereby the marginalized subject is undermined as a knower. The secondary harm Fricker identifies is that of “cognitive disablement”:Madness and Civilization, Foucault defends the urgent need for such a genealogy due to the breakdown in communication between these two groups:The constitution of madness as a mental illness … affords the evidence of a broken dialogue, posits the separation as already affected, and thrusts into oblivion all those stammered, imperfect words without fixed syntax in which the exchange between madness and reason was made. The language of psychiatry, which is a monologue of reason about madness, has been established only on the basis of such a silence.. According to the APA, the aim of the latest edition of the DSM is as follows:[to create] a common language for clinicians to communicate about their patients and [establish] consistent and reliable diagnoses that can be used in the research of mental disorders. It also provides a common language for researchers to study the criteria for potential future revisions and to aid in the development of medications and other interventions(DSM-5).Healthcare professionals attempted to overcome the inevitable communication barriers posed by psychiatry through the development of a universal psychiatric vocabulary. This universal vocabulary took the form of diagnostic manuals, the most popular today being the patient. By emphasizing communication about patients rather than to patients, the APA suggests that the patient’s understanding of their psychiatric illness is secondary to that of the clinician and researcher.Whilst the DSM may go some way toward creating a universal framework for understanding psychiatric illness amongst healthcare professionals and researchers, what is missing from this mission statement is the pursuit of a common language between clinician and Thus, despite the central role the doctor-patient dialogue plays in psychiatry, the voice of the patient is notably omitted from diagnostic manuals. Instead, an epistemic privilege is afforded to the third-person perspective of the DSM and the psychiatrist who mediates it: “the medical perspective is regarded not only as authoritative but often even exclusive of other perspectives, such that medical diagnosis effectively constitutes a monopoly on the way the experience is interpreted” .The upshot of such hermeneutical injustice can be found in Stanghellini and Mancini’s analysis of the “structured clinical interview” or “technical interview”, the interviewing method developed by Spitzer for assessing psychiatric symptoms. The structural clinical interview, combined with the diagnostic criteria of the DSM-5, make up the diagnostic process Stanghellini and Mancini refer to as “the technical approach”  is decided Following Fricker’s account, the unequal hermeneutical participation of a marginalized group from “some practice that would have value for the participant”  leaves a depleted pool of hermeneutical resources Fricker, , p. 153.To understand the phenomenological impact of hermeneutical injustice in psychiatric healthcare, let us turn to Merleau-Ponty’s concept of “movement toward the possible” . In the words of Styron, “I began to experience a vaguely troubling malaise, a sense of something having gone cockeyed in the domestic universe I’d done so long, so comfortably” Styron, , p.41. TWithout speech expression, the person with psychiatric illness cannot throw their body into an act of free and open expression in the same way as their hermeneutically privileged counterparts. For example, in recounting his vain attempts to communicate with his psychiatrist, Styron describes such phenomenological deterioration in his speech expression: “my speech, emulating my way of walking, had slowed to the vocal equivalent of a shuffle” Styron, , p. 55. Without the capacity to express one’s illness experience, the hermeneutically marginalized lose an essential way they were tied to the world. Unable to exploit the hermeneutical resources that once rolled off the tongue, engagement with their environment is strained. The environment no longer invites interaction in the way it once did. In this sense, the hermeneutically marginalized subject suffers an “unworlding” as the look and feel of the world is altered. Through a phenomenological perspective, it becomes clear that the unequal hermeneutical climate of psychiatric healthcare perpetuates, and even exacerbates, this experience of “unworlding” for the person with psychiatric illness.but rather the distinct feeling of being unheard” .distressed that I was losing a sense of wholeness, splitting apart the young woman whose religious and existential crises had precipitated a desperate self-assault and the young woman who pretended that group therapy was interesting and helpful in order to move a notch further toward her dischargeA gulf widened between the self I was able to be outside the hospital and the self I had to present inside. I spoke as I knew I had to in order to be heard, aware of the dishonesty that saturated every obeisance and . As Steslow observes, oppressive hermeneutical practices that force psychiatric patients to mimic a remote medical voice “may end by creating minds more fragmented in Steslow, , p. 30. A further consequence of hermeneutical injustice is a loss of not only one’s capacity for an essential form of embodied expression, but also a loss in one’s intersubjectivity. A breakdown in intersubjectivity is a common feature in psychiatric illness. For example, in depression “an overarching theme is that a type of interpersonal connection, which most people take for granted in the course of everyday life, no longer seems possible” . Thus, recovery of speech expression is necessary  to restore one’s being-in-the-world. Once the patient’s capacity for speech expression is restored, there is hope of paving the way toward a coherent and more comfortable lived experience, whereby their interactions with objects and others become as inconspicuous and natural as before.Through this paper, I have highlighted how hermeneutic strategies in psychiatric healthcare can either ameliorate or exacerbate the experience of “unworlding” for the person with a psychiatric illness. Hermeneutical injustice occurs in psychiatry when the interpretive framework obstructs the patient from understanding their illness-experience because it champions the third-person perspective of the healthcare professional. As such, the patient’s own understanding of their illness is omitted from the collective, clinical understanding of their condition. This is no small loss, as Merleau-Ponty observes that speech expression is a function of the body schema that allows “the human body to celebrate the world and to finally live it” (Merleau-Ponty, Hermeneutical injustice, in turn, elicits an “unworlding”. The person with psychiatric illness experiences the hermeneutical deficiency as an unexpected absence in their field of experience. Although the intention toward speech expression boils beneath the surface as the person longs to put their experience of psychiatric illness into words, this intention cannot be transformed into action as the necessary hermeneutical resources are missing. Consequently, the person’s movement through the world is stunted due to this gap in one’s system of anticipation. This too has a profound impact on one’s ability to form a social whole with Others, thus further entrenching a gap between the person with psychiatric illness and the world.On these grounds, I conclude that hermeneutical injustice entrenched in the practices of psychiatric healthcare, contributes to, and perhaps even intensifies, the experience of “unworlding” for the person with psychiatric illness. As such, there is a two-way relationship between unworlding and ineffability in psychiatric illness.


Fundamental studies have improved understanding of molecular-levelproperties and behavior in surfactant-oil-water (SOW) systems at equilibriumand under nonequilibrium conditions. However, confusion persists regardingthe terms “microemulsion” and “curvature”in these systems. Microemulsion refers to a single-phase system thatdoes not contain distinct oil or water droplets but at least fourdifferent structures with globular domains of nanometer size and sometimesarbitrary shape. The significance of “curvature” insuch systems is unclear. At high surfactant concentrations , a single phase zone has been identified in whichcomplex molecular arrangements may result in light scattering. Assurfactant concentration decreases, the single phase is referred toas a bicontinuous microemulsion, known as the middle phase in a WinsorIII triphasic system. Its structure has been described as involvingsimple or multiple surfactant films surrounding more or less elongatedexcess oil and water phase globules. In cases where the system separatesinto two or three phases, known as Winsor I or II systems, one ofthe phases, containing most of the surfactant, is also confusedlyreferred to as the microemulsion. In this surfactant-rich phase, theonly curved objects are micellar size structures that are solublein the system and have no real interface but rather exchange surfactantmolecules with the external liquid phase at an ultrafast pace. Theuse of the term “curvature” in the context of thesecomplex microemulsion systems is confusing, particularly when appliedto merged nanometer-size globular or percolating domains. In thiswork, we discuss the terms “microemulsion” and “curvature”,and the most simple four-dimensional spatiotemporal model is proposedconcerning SOW equilibrated systems near the optimum formulation.This model explains the motion of surfactant molecules due to Brownianmovement, which is a quick and arbitrary thermal fluctuation, andlimited to a short distance. The resulting observation and behaviorwill be an average in time and in space, leading to a permanent changein the local microcurvature of the aggregate, thus changing the averagefrom micelle-like to inverse micelle-like order over an extremelyshort time. The term “microcurvature” is used to explainthe small variations of globule size and indicates a close-to-zeromean curvature of the surfactant-containing film surface shape. The science of soap-making has evolved over the past 4000years through trial and error, eventually leading to a better understandingof the molecular mechanisms behind cleaning at interfaces. The studyof surface and interface science, including the physical and chemicalaspects of adsorption, wetting, adhesion, friction, and mono- andbilayer films, has involved the investigation of intermolecular forcesin colloidal dispersions by renowned scientists such as van der Waals,Keesom, London, Langmuir, Debye, Huckel, Boltzmann, Derjaguin, Landau,Vervey, Overbeek, Miller, Hirasaki, and others. Physicists includingEinstein and Smoluchowski also made important contributions predictingBrownian motion through the study of molecular fluctuations, whichwas later confirmed experimentally by Perrin, who received a NobelPrize for his work. These fundamental studies have improved our understandingof the forces at play at the molecular level and have led to the developmentof the field of colloid and interface science, which aims to providea theoretical framework for practical applications.In the early1900s, the introduction of new amphiphilic moleculeswith polar groups other than those found in soaps, such as ionic sulfateand sulfonate groups and nonionic polyethoxylated chains, expandedthe surfactant-based cleaning formulations into a wide range of applications.These molecules, which were less sensitive to precipitation by polyvalentcations commonly found in washing water, were no longer referred bytheir tension-reduction properties, like “tensioactif”in French and “tenside” in German but were definitivelyrenamed surface active agents (surfactants) in 1950. This happenedin industrial research centers, particularly in the United Stateswho started to publish not only knowledge but also some know-how information,often in relation with commercial products. Over the following halfcentury, there was significant growth in the surfactant business witha divulgation increase through conferences on specific topics, particularlyenhanced oil recovery (EOR).6 most of the review books have beenwritten by multiple authors, resulting in discrepancies between differentsources and even between chapters within the same book. One of thesediscrepancies is around the term “microemulsion” andthe multiple meanings of the word “curvature”.12 As stated by Rosen in his courses13 andin the preface of his exceptional book on practical applications ofsurfactants,14 these disagreements andinconsistencies are probably due to the strong differences existingbetween theoretical knowledge and practical know-how. Rosen’scomments essentially mentioned that this situation has reached thepoint where nobody can be a specialist in both approaches at the sametime.This expansion led to the publication,starting in the late 1970s,of over 200 books and encyclopedias and thousands of articles withthe contribution of numerous authors, not only from the academy butalso from industry. With very few exceptions like the sometimes called“surfactant science bible” written by Milton Rosen firstin 1978 with 300 pages, and now in its fourth edition with a doubledsize,1 making it impracticalto review and assimilate all the available information in less thanthree years of full-time study. Consequently, only a partial formationcould be carried out for individuals who are going to be involvedwith the use or formulation of SOW systems, such as tutorial activitieswith a limited time like 2–3 courses with 50–60 h peryear. This presents a challenge for effectively teaching individualsabout surfactants, colloids, and interfaces, and many researchersin these fields are likely unaware of important issues due to thisinformation overload. This has practical consequences for the fieldas a whole.The main issue is that since the 1990s the amount of availableinformation in both types of approaches became excessive, as shownin a recent review,6 the “microemulsion formulation review” by M. Bourreland R. S. Schechter,15 and the very recenttutorial screening on “emulsions, microemulsions and foams”by D. Langevin,3 who included both wordsemulsion and microemulsion in the title, thus clearly indicating thatthey have different meanings. The other selected books on “microemulsions”in their title were edited by notable contributors like L. Prince,16 K. L. Mittal,17 M.Fanun,18 P. Kumar and K. L. Mittal,19 C. Stubenrauch,20 L. E. Scriven and K. L. Mittal,21 R.Zana,22 and J. N. Israelachvili.23There are over 50 books with the term “microemulsion”in the title, over 150 books that have at least one chapter with thisterm in the title, and more than 500 journal articles that use thisterm. However, many of these publications are limited to theoreticalconcepts or applications and contain misleading or nongeneralizedcomments, as well as repeated confusion. The following list of tenworks represents a carefully selected bibliography for readers ofthis review to understand the challenges surrounding the nomenclatureand meanings of microemulsion mesophase structures and curvature.Only three of these were written by authors in a very consistent waylike the fundamental and practical basics in “surfactant scienceand applications” by M. J. Rosen,24 included in the first chapters of his earlybook16 a partially fair discussion aboutsome disagreements regarding the use of this term. This early textis worth reading, particularly because it was relatively simple withmuch less experimental techniques than recent works. The book fromD. Langevin3 presents a review of conceptsand advanced experimental techniques, as well as an overview of currentmodels’ alternatives. It is worth noting that this remarkabletext clearly mentions that there are ongoing debates regarding theuse of the term “microemulsion” and the nature of themesophase structures.These selected references include themost influential opinionsand some controversies on the topic of microemulsion structures andcurvature meanings in the last 50 years from the most productive researcherson the topics who presented talks at numerous conferences. L. Princewho coauthored the first article proposing the term “microemulsion”,In the present review, we address themisleading use of the term“microemulsion” and the multiple meanings of the word“curvature” depending on the adjective used to modifyit. We present a simple model for the structure of SOW systems atthe so-called optimum formulation, where highly specific and usefulproperties can be found in both equilibrium and dynamic situations,such as in emulsions.While useful, the references cited inthis review represent onlya small fraction of the vast literature on this subject in reviewbooks and articles on the basic knowledge and know-how from originalcontributions to critical advances. This does not imply that all thenot-cited publications are unsatisfactory but that there is an overwhelmingvolume of published material and that the purpose of this review isnot a full review of literature work that has been divulgated. Instead,this review focuses on presenting the basic behavior of simple SOWsystems with sufficient information to understand how certain inappropriatenomenclature has contributed to confusion in the field.26 The addition of a thirdcomponent type, i.e., an amphiphilic structure with two differentparts (and thus a double affinity), does not allow using the HSP approach.Surfactants, referred to as C by the Winsor original model,27 are molecules that at least contain a polargroup called “head” with some hydrophilic affinity toa water phase  and a nonpolargroup, generally a hydrocarbon called “tail” that hasa lipophilic affinity for the oil phase . Consequently, surfactants may be soluble in waterbecause of their headgroup, in oil because of their tail, or in bothwhen the two affinities are more or less balanced.Oil and waterare incompatible liquids that cannot be mixed intoa single phase, and this situation can be represented by the Hansensolubility parameters (HSP) that numerically indicate the differencein polarity of two substances.Accordingly,surfactants can best satisfy their double affinitypositioned at the interface, and thus the surfactant interfacial adsorptionis the crucial feature. When the oil–water interfacial areais fully covered, the extra surfactant separates or, in most cases,goes to the phase having the higher affinity for it.6 For instance, above the Kraft point, the ionicsurfactant either precipitates or solubilizes under the form of aggregates,known as micelle in water with typically 50–100 molecules andwhose radius is about the size of the amphiphile straight or benttail, around 1–2 nm. The same effect happens with the excesssurfactant in oil with the occurrence of the so-called inverse micellestructure that is often smaller. This aggregation tends to removethe incompatible part of the surfactant from the solubilizing phase,at a concentration called the critical micelle concentration (CMC),extensively described in the literature, in particular in tutorialbooks or booklets.28 The CMC is generally a smallconcentration but very dependent on the surfactant structure, notonly the tail length but also the headgroup. For instance, it is about0.008 mol/L in water for a hydrophilic ionic surfactant like sodiumdodecyl sulfate. However, it is much lower, around 0.00006 mol/L,for another water-soluble specie like dodecyl pentaethoxylate, becauseof the importance of head structure on aggregation. Its decimal logarithmdecreases almost linearly with the number of carbon atoms in an alkyltail and also increases linearly as the ethylene oxide number of anethoxylated nonionic increases.29 The CMC is also verysensitive to external effects of solubilization in solution, likethe salinity and hardness of the aqueous phase and the temperature.However,since the surfactant always has a part that does not presenta good affinity for the oil or water phase, the usual solubility assingle molecules has often a (low) molecular concentration limit,which is in general related to temperature as the minimum Kraft pointfor ionic species or the cloud point for nonionic ones.30In the presence of both oil and water in the system, the surfactantmolecule has a preference in its partitioning and is mostly in oneof them. This occurs usually as a single phase solution of micellesor inverse micelles, with the other (excess) phase containing verylow residual surfactant concentration at or below the correspondingCMC.31 proposed the ratioof affinities R = ACO/ACW as the numerical criterion, withan exact balance of affinities of the surfactant in oil and waterwhen R = 1. It was a single term criterion like theempirical HLB value of the surfactant6 orthe surfactant critical packing parameter CPP at the interface,32 but many studies indicated that the interactionsat interfaces also involved different other terms to be estimated,such as the oil nature, the brine salinity, the temperature, and thepressure. In the early 1970s, the commercial influence of enhancedoil recovery (EOR) led petroleum companies and government/universityR&D institutes to rediscover Winsor’s previous work. Theystarted to consider the equivalence of the interaction ratio R = ACO/ACW = 1 to a zero chemical potential difference written as theso-called surfactant affinity difference SAD = ACO – ACW = 0.33In a system containing surfactantin both water and oil, the phasebehavior is determined by the surfactant affinity balance for oneof the phases. Since the affinity is the negative of the chemicalpotential, it has to do with the molecular interactions, attractiveor repulsive. WinsorThe calculation of the ratio or differencein affinity is complexeven in very simple cases, in particular because of the many differentphenomena and variables involved. Also, the different assumptionsconcerning the interactions play a role, sometimes in disagreementsin some theoretical or experimental approaches. It can be said thatthe considerable published knowledge, even now, does not allow oneto accurately calculate a value of the chemical potential ratio ordifference and that the corresponding variables to be used in thetheoretical aspects are not easy to handle and measure. Winsor’sproposal was the first suggestion using a set of several practicalformulation variables, while the other approaches are dealing onlywith one descriptor of the system’s behavior.34 and represented the proportionof the surfactant having a preferred affinity for water, strongerthan for oil, i.e., corresponding to a negative SAD value. It wasa very good name, but it was only calculated with an approximate relationlike the 1/5 of the wt % of the poly(ethylene oxide) group for alcoholethoxylates. The other proposal known as the surfactant critical packingparameter (CPP)23 was an extension of thevery early wedge theory35 that used a representationof a conic association plug of surfactant molecules with water andoil aggregated into a micelle, reverse micelle, bilayer vesicle, ormultilayer flat or curved liquid crystal, and the so-called “microemulsion”.This last name was a new nomenclature that produced a confusion becausethese systems, particularly the bicontinuous type that does not containreal independent oil or water small drops but domains with arbitraryshape and curvature significance, logically labeled “crazymixed-up stuff” by Scriven in a chapter of his book.21 One of the confusions was also using the samecurvature meaning for the micellar surfactant aggregation (1–2nm size) and an actual emulsion liquid drop  for which the wedge theory cone model cannot have logicallythe same influence, as mentioned by the author Harkins in his originalpublication.35The firstrepresentative parameter was called the surfactant hydrophilic–lipophilicbalance (HLB)n-alkane) ,and the temperature and the surfactant nature .37 Some other variables were knownto be important candidates to participate in describing specificationsof a petroleum reservoir system, such as pressure (downhole), andthe composition and surfactant concentration Cs, as well as alcohol type and concentration,if present. Thus, it is evident that even in a very simplified case,there were 8 variables, and thus using a single variable criterionlike in HLB or CPP is obviously not enough.In the 1970s, thereported practical variables in a crude oil reservoirwere very easy to understand and measure in a first simple equivalentmodel. They were the water phase nature ,the oil nature ACN .24 and Scriven added the “bicontinuous”adjective to satisfy the found evidence.40 However, even if it appears to be between WI and WII types, thisWIII middle phase cannot be logically represented as a mixture ofmicelles and inverse micelles, as proposed recently,41 since these aggregates in WI and WII cases have differentexternal solution phases.The WIII type looks as the intermediate betweentype WI and typeWII, and is a very specific case as far as the formulation is concerned,but it does not necessarily indicate a clear middle phase structurecharacteristic. This phase is now generally called “bicontinuousmicroemulsion” since Schulman proposed the term “microemulsion”In type IV phase behavior, the percentageof the phase containingthe surfactant has increased to the whole volume. It could be becausethere is more surfactant in the system or because there is more solubilizationof the excess water or/and oil in the phase containing surfactantin any type case, in particular in the WIII type.42 used at firstthe term “transparent oil-water dispersion stabilized withsoap and alcohol” that corresponded to the evidence at theirtime.It is notknown whether the middle phase is a water or oil solutionand how much it contains of both and how, and this is probably whySchulman and colleaguesWinsor’s 1948 original studies were meant to determinethephase behavior change when there is a variation in one formulationvariable that alters the ratio R of interactions of the surfactantwith oil and water or its surfactant affinity difference SAD.RT44).47It is seen that in the middle of the scan, thereis a salinityrange in which a WIII three-phase behavior is obtained in the testtubes. This corresponds to a Winsor SOW diagram with a triangularthree-phase zone (3ϕ) surrounded by three biphasic zones (indicatedas 2ϕ), the extremely narrow one just below the 3ϕ trianglenot being shown. This kind of representation has been published inmany places, and the reader not familiar with it can check the literature.The picture in The test tubes scan also indicates the solubilizationvariationin the surfactant phase in the type I and type II zones, accordingto the remaining volume of the excess phases. The schematic drawingsbelow the diagram indicate the usually proposed structure of the singlephase containing most of the surfactant, i.e., swollen micelles intype I and type II zones and a so-called bicontinuous microemulsionstructure in the type III zone.48 and his calculation with a simple flat structure model.4950 It is also called the optimum formulation for emulsion breakingin processes such as crude oil dehydration54 because of the correspondingemulsion stability minimum shown in This central value of the WIII zone inthe formulation scan isthe so-called optimum formulation for enhanced oil recovery becauseit corresponds to the minimum tension as seen in 57This trend of phase behavior change (WI > WIII> WII or inverse)with a continuous variation of a formulation variable was found tobe qualitatively general by Winsor and the following researchers,with any of the variables susceptible to alter one interaction ofthe surfactant with oil and water , andthus R, SAD, or HLD.2However, many cases aremore complex than the presented examplein the previous 59The second issue to be considered with 63 This variation of aggregate size and nature may alter the interpretationof some measurements, particularly for the size, shape, and curvaturemeaning of existing mesostructures.The third issue is that the aggregationstructure to solubilizethe surfactant molecules at high surfactant concentration may be quitedifferent from a spherical micelle with a 1–2 nm radius. Ithappens not only for pure selected systems but also in many practicalcases. For instance, in a crude oil/brine system, asphaltene moleculesare very lipophilic surfactants that associate first at very low concentrationsin 3–4 molecules small micellelike aggregates or as multimicellesmuch bigger, known as clusters, when their concentration is higher.How much higher depends on the maltenes nature , temperature, and pressure.64 and later Kahlweit and Strey,65 with similarity with previous studies carriedout by people from industry research on practical cases like EOR,70 which were published in completely different kinds of conferencesand journals, and with a different approach, in particular the selectedscanned variable. Additional confusion came from arbitrarily changingthe previously used logical terminology in SOW systems, calling thewater A, the oil B, the surfactant concentration γ, etc.6568 or the ethoxylation effect for the nonionicsurfactants head (EON).71 The oil ACN,which was the first to be historically used for a formulation scanin the University of Texas group,72 comparedwith the interaction with the surfactant alkyl tail length SAT, andresulted in a general equation for all cases,73 is thus probably the simplest theoretical formulation scan. Nevertheless,it must be noted that the results indicated in In most theoretical studies, the temperatureis generally the onlyformulation variable to be used. This has some advantages, such asthe possibility of increasing or decreasing it without making newsystems, but also some inconveniences such as the range limits, andthe fact that temperature alters essentially all interactions, thusmany different effects are to be discussed. On the contrary, the salinityonly changes the interaction of water with the surfactant head,Micelles in W or inversed micellesin O are located on the leftand right sides of the diagram at a low surfactant concentration,but above the CMC. Their shape is mainly spherical, exchanging surfactantmolecules in permanence with the saturated molecular solution. Whenmore surfactant is added, the number of micelles increases. For apure surfactant, there is essentially no change in the micellar arrangement,but in some cases, other types of structured arrangements can be formedand/or coexist. When the representative point enters inside the diagram,i.e., in a zone with both water and oil content, the micelles solubilizethe lower content phase inside and are then called swollen micellesbecause their size increases  would be clearer, even if it is still misleadingbecause there is no interface as in a real emulsion. Consequently,it can be said that the structure of this middle phase M, and thesingle phase found above it, is still uncertain and depends on theinterpretations of results with different instrumental techniquesor methods described in many publications. The best review with manycollaborators75 indicated weak and strongarrangements with more or less rigidity or flexibility with differentliquid crystal (LC) and microemulsions labels.76 In the single-phase zone called 1ϕ, microemulsionabove M and bimodal curves, the actual structural changing of WORor surfactant concentration will eventually stay homogeneous withsome variation in light scattering but not up to the typical whitishaspect of classical emulsions.Below thesetwo diphasic zones (2ϕ), there is a triphasictriangular zone (3ϕ) in the WIII diagram that separates in a“central” surfactant-rich middle phase microemulsion(M) having an aggregation mesostructure, and two O and W excess phases.Above these three multiphase zones (2ϕ and 3ϕ), thereis a large single-phase zone close to the upper boundaries of thetwo-phase zones, which has also been called a microemulsion. Nevertheless,it is essentially known that it does not contain ultrasmall oil andwater droplets, as proposed by Schulman in 1959,77 or microstructure.78 Other studies have indicated that liquid crystalstructures with more or less flexibility, depending on the amountof oil or water inside, can occur with a more or less organized arrangementwith hexagonal, cubic, or lamellar shapes.79 Such structure can have a network of slightly organized surfactantmolecule zones like cylinders or wormlike cylinders, cubic arrangement,lamella, bent layers or bilayers, vesicles, and completely disorganizedshape domains of almost pure water and oil zones, but not with sphericalshape.The conductivity variation fromleft to right in the It can be said that there is a continuous transitionin the upperpart of the (1ϕ) zone, sometimes with a precipitate formed asrigid crystal structures at very high surfactant concentration, asindicated in In microscopic studies performed in the past century, the dropsof the emulsions were mainly spherical (or only slightly deformedwhen subjected to shear or dilation) in a size of several micrometers.Mechanical stirring is usually required to produce an emulsion froma SOW equilibrated system at some surfactant concentration. Energyis required in emulsification because it is linked to the increasein surface area with the γΔA term, that is significantunless the tension is extremely low, as it happens close to optimumformulation. Spontaneous changes tend to reduce the surface area andthus to coalesce separated drops, making an ordinary emulsion notthermodynamically stable, even if the breaking time scale can be verylong.81 in scans performed with ethoxylated surfactants systems with thetemperature as the formulation variable. In numerous Shinoda’spublications, there was no citation of Winsor’s work published15 years before, nor the name microemulsion proposed by Schulman 10years before. The only other study mentioned by Shinoda’s groupwas the Griffin HLB single variable concept.82 As far as the phase behavior was concerned, it was shown not ina Winsor ternary diagram but in other bidimensional diagrams, includingthe formulation variable temperature and the composition WOR,83 as will be discussed later.Emulsions in SOW systems contain a water phase with highelectricalconductivity and an oil phase that generally is not conducting. Thus, dependingon the type of external phase, the conductivity is high or low. Microemulsionsshow smooth conductivity variation in a formulation or WOR scan. Incontrast, emulsions exhibit a marked change in conductivity aroundthe inversion point, for instance, when it changes from O/W to W/O,at the so-called phase inversion temperature (PIT)The microemulsionname and its relationship with other variablessuch as salinity or surfactant type as in EOR were only publishedin the 1980s, i.e., 30 years after Winsor’s work, and just2 years before Kahlweit and Strey’s group started to extensivelyenter this scientific area insisting on the scanning with temperature.This situation is noted here because comparing different approachesprobably started only at this time, but still with temperature asthe most used formulation variable in theoretical studies.Asdiscussed in detail above, the microemulsion was a confusingnomenclature incorporating the “emulsion” term, becauseit is a single-phase system, indicated (1ϕ) in At this size level, the only curved object is the micelle or inversemicelle found in type I or type II surfactant phases, with a shapeclose to a sphere. But micelles are water or oil soluble and havethus no real interface and do not coalesce, unlike emulsion dropletsthat are typically much larger. Moreover, micelles are stable becausethey avoid the precipitation of the surfactant. Additionally, micellesare always exchanging surfactant molecules all the time and very fast.P = 2γ/R equation, where γ is the interfacial tension and R the radius of the sphere. When two drops are bumping, the smallone has a superior pressure and thus coalesces sooner or later intothe larger one. Consequently, the drops tend to become larger untilthey are all coalesced in a single phase. This does not happen withmicelles because two bumping ones do not coalesce to make a biggersingle one. There is no such pressure variation from the inside tothe outside of a micelle, the interfacial tension is not measuredat the micelle surrounding but at an interface. Micelles just canappear or disappear depending on the surfactant molecules' permanentquick exchange with the solvent/external phase.In a different situation, emulsion drops are in the 1–10μm size with internal pressure higher than the external fluidas indicated by the Δ85 The deformation from sphere is due to the presence of oil and waterglobules with other shapes, sometimes variable from place to placeas in quasi-crystal structures filling the whole volume with multifaceteddomains.86 In such cases, the word curvaturethat is simple to understand for spherical drops or spherical micellesis confusing to apply with stable thermotropic or unstable lyotropicliquid crystals or microemulsion globular domains that are more orless merged, as shown in 87As indicatedin 79 as well as a review article on mesophases thatthe reader should check if the book is too long.88 This clear article is enough to understand the confusionon curvature concepts for dispersed globular objects found in bicontinuousmicroemulsion and sometimes called a sponge structure. It is worthnoting that, in general, these structures are not containing exactlyrepetitive shape domains, in particular with a zero mean curvaturesplay saddle shape, aspects already mentioned in Scriven’soriginal article77 with their correspondingpatterns89 and relation with low interfacialtension.90A book containing amazing drawings concerning thecurvature ofstrange surfaces with saddle shape aspect has been published by Hyde92 It happens in certain mediterranean aperitifslike the Greek ouzo and the French pastis containing a large amountof a low molecular weight amphiphile, e.g., 40–45% of ethanol,only about 1–2% of a terpenoid oil very insoluble in waterlike anethole, and slightly more than 50% water. These anis-flavoredliquors are clear but become cloudy when excess water is added. Themechanisms behind the effect are not fully understood in particularbecause the oil phase is in a very small amount, not at WOR closeto unity as in typical microemulsions in the center of a ternary diagram.94 Eventual aggregates of molecules can create structures or a solutionwith no structure at all that allows for the formation of a continuous,transparent phase.93 The whitening of theouzo or pastis drinks when water is added may be just a solubilitylimit when the ethanol content goes below 30%. These systems are oftenreferred to as surfactantless microemulsions,97 although thiscan be misleading because they differ significantly from traditionalmicroemulsions formation,98 thus addingeven more confusion to the terminology.Other terms such as “surfactantlessmicroemulsions”have been confusedly used for systems where the so-called Ouzo effectoccurs.24 particularly when smaller than 1/10 of the wavelength,e.g., 0.05 μm (50 nm), for the sunlight. However, objects thatare not spherical, particularly percolated micelles or wormlike orcylindrical globules, can produce inaccuracies and confusion aboutthe curvature term meaning.The name curvature has been used in emulsion systems with a typicallyspherical interface in type I and type II cases with drops of essentiallypure oil or water liquids of about 1–10 μm, eventuallyin a wider range in scales. In all cases, the natural light scatteringis very strong and the emulsions are very opaque. Schulman selectedthe name microemulsion because of the known trend that much smallerspherical objects exhibit very little light scattering,There are several issues producinginconsistencies with the sameterm: (i) Understanding what is a curvature of a line in a bidimensionalspace is simple because there is no alternative to the center of curvatureand the bending concept. In three dimensions, it is not the case fora surface shape very different from a sphere because the immediatefeeling is that there are variable curvatures, depending on how thesurface is cut by a plane to produce different 2D curved lines. Thename “mean” curvature requires at least two curvatures,i.e., two cuts of the surface, which are somehow arbitrary, mostlytaken as coming from the more curved and less curved 2D cuts, a choicethat is not evident. (ii) Looking at Moreover, the problem of curvature significanceis unlikely whenthe surface is the interface of two immiscible fluids phases. Forinstance, for a cylindrical liquid stream, the two different curvaturesare not happening but only temporarily. As a faucet is opened an almostcylindrical stream of water is produced with a diameter that decreasesbecause of the gravity. It then quickly becomes a series of droplets,with the radius depending on several parameters, and showing a strangeresult in which the surface area increases because of the work producedby gravity motion.P = ρgh = 2γ/R equation at the interface. When two drops are bumping,the difference in pressure inside them produces the small one emptyingin the large one by different mechanisms. When two micelles are bumping,this does not happen. This is probably because the micellar solutionhas no interface and no difference in pressure between the insideand outside. In fact, a micelle does not empty into another biggerone, i.e., they do not coalesce. This is because micelles are surfactantaggregates, and what is in motion are the molecules exchanging withthe external solution or displacing their position in the arrangementstructure if there are not spherical aggregates. Therefore, a microemulsiondoes not change with time but at the molecular level keeping the sameaverage balance of interactions.The curvature has importance on the differenceof pressure on thetwo sides of an interface. The typical rising and curving of the interfaceat the vertical wetted wall or a thin capillary cylinder clearly indicatesthe meaning of the Δ100In a normal drop size, anyshear will produce elongation, thusthe interfacial area and the pressure difference in the drop willreestablish the spherical shape spontaneously when the shear disappears.This will be a much shorter variation than the interdrop film thinningas in the Marangoni effect elasticity.101 However,it was seen in Thesecond confusion concerns the association of the transparency-opacitywith the microemulsion name and domain size, spherical or differentfrom it. For spherical objects in the micrometers range, i.e., closeto the light wavelength, the opacity is reduced when the dropletsare getting smaller, and this is consistent with the use of the microemulsionname. The issue is that this might be a misperception because if themicelles get more swollen as it happens when the formulation approachesthe optimum in type I and type II phase behavior then they becomebigger and are more likely to be more whitish (or less transparent)because of light scattering.Nevertheless, for this middle phase microemulsion, themore opaqueor whiter it is, the higher the solubilization parameter and the lowerthe interfacial tensions. This is seen in The interfacial tension value for the fourth (right)case is verydifficult to measure and quite approximate (±30%), but the factthat it is more whitish than the third one clearly indicates a lowertension and a higher solubilization (that is very close to 100% ofoil and water with only 15 wt % of extended surfactant).Thiskind of formulation is quite appropriate for EOR, pharmaceuticalcreams, dehydration, and other practical cases.104 It thus means thatthe exact position of the optimum is extremely sensitive to the formulationscan value.It is worthremembering that when increased performance is produced,as seen in C = 1/R that is the only obvious one inthe two-dimension flat space. In one of the well-known examples ofthe confusion, a so-called characteristic curvature of a surfactant(CC) term is used,105 the curvature isdefined essentially from the oil/water solubilization at a WOR = 1.It is obtained by calculating the ratio of the oil volume  to the surfactant volume, thatis a layer on top of the spherical oil or water domain.The curvature concept with an usual emulsion isessentially a temporaryvalue, i.e., the inverse of the drop’s radius. Consequently,it will change with time as well as with the energy introduced tomake the emulsion, e.g., the stirring apparatus and work input. Onthe contrary, the curvature in a microemulsion with very small domainsis supposed to be a constant independent of the formation story, andof the stirring, whatever the mixing process. However, it dependson the way the curvature is calculated. For a sphere, it is withoutconfusion, but for a domain that is not a sphere, it can be confusingbecause it depends on the way the curvature is defined as overall,partial, spontaneous, intrinsic, etc., or by a formula which is not oil or volwater = 4/3 πR3 and volsurf = 4πR2L, where R is the radiusof the oil or water sphere and L is the thicknessof the surfactant layer.VolR/3L, where R is the radius of the spherical oil or water domain and L is the thickness of the surfactant layer around them.The ratio, basically the performanceof the WIII system with equaloil or water solubilized in spherical domains , is SP= L = 1 nm, as is the case for dodecyl sulfateand a measurement of solubilization performance SP = 5.5 and γ= 0.01 mN/m, a radius of 15 nm is indicated. If SP = 17 and γ= 0.001 mN/m, a radius of 50 nm is obtained, which is probably aswhitish as would be expected from a 0.2 μm nanoemulsion. Thus,the opacity of the emulsion or microemulsion is not very unique information.For At each indicated point (a to f) of the triangularSOW diagrams,there are two representations of test tubes, the left (ϕB) beingthe aspect of the equilibrated system and the right one (SS) beingthe aspect of a just stirred system, i.e., the emulsified case. Atthe square or circular white points indicating the composition-formulationof systems a, b, and c, the equilibrated and recently stirred systemsexhibit the same aspect, because there are single phases with objectstoo small to result in a whitish color. Note, however, that if theM point is not far away from the base of the triangle, a single phasehappens at a low surfactant concentration. But in any case, the bluishcolor will be the same for the equilibrated and stirred systems.On the contrary, in the black points d, e, and f in the polyphasiccases types I, II, or III, there are 2 or 3 phases, resulting in theformation of emulsions with a whitish color that are much whiter thanthe equilibrated surfactant microemulsions, whatever the surfactantis in oil, water, or middle phase.107Information on the conductivityis easy to handle with an emulsionwith drops of one phase dispersed in the other continuous phase. Emulsionconductivity is measured under stirring, thus homogeneity to avoidseparation of different phases is attained because of different densities,and the inversion is easy to detect with very quick conductivity changeover a very narrow range in the scan. Shinoda’s temperaturescan fairly showed this phenomenon in nonionic surfactant system atthe optimum formulation called the PIT.In the a-b-c scans in the previous 108 found thatthe WIII case at equilibrium was essentially at the same formulationas the PIT but that it was theoretically something different. Thus,they called it HLB-temperature as far as phase behavior was concerned.Later Shinoda and KuniedaThey did not say it, but they probably found out that a WIII formulationwas attained and that they were two cases, one in the 1ϕ zoneand one in the 3ϕ zone. When they were stirred, the aspect ofthe first one (1ϕ slight turbidity blue color) was kept, whilethe 3ϕ system was becoming extremely white as seen in As shown in 110 This is indicated as a sum up in In a WIII case, the three-phase emulsion consistsin drops of excesswater and excess oil in an external phase that is the middle phaseM. Thus, there are two emulsions, i.e., W/M and O/M, and they breakquickly at the same time but often one quicker than the other dependingon the formulation with respect to the optimum, as shown in the 1980s.Therefore, with a three-phase emulsion, the stability is measuredas the velocity of separation of excess phases, excess oil in theupper part and excess water in the lower part. However, observingthe separation of oil in an O/M emulsion or the water in the W/M indicatesthey are essentially the same with both O and W drops elongated whenmoving in the remaining emulsified center zone.S = 9.5%, the phase behavior is WI and the two-phaseemulsion is O/W. Above this value, the emulsion becomes O/M, and itsminimum is at a salinity slightly lower (S = 10.5)than the center of the WIII range S = 11.3%, whichis indicated as the optimum by a black arrow. On the other hand, ata salinity above the upper limit of the WIII zone (over S = 13.5%), there is a WII phase behavior and a W/O emulsion thatbecomes a W/M emulsion in the triphasic zone. It is also seen thatthe minimum stability of the W/M emulsion is found at S = 11.8%, slightly above the optimum formulation.At salinitybelow the value corresponding to WIII zone, i.e., lowerthan Thus, theoptimum formulation where the interfacial tension betweenexcess O and excess W is minimum, is found at the crossing point ofthe stability curves of the O/M and W/M emulsions. Therefore, if amixture of the three phases is stirred, the formed emulsion separatesboth oil and water and the figure curves can be drawn as in It is worthnoting that with very low interfacial tension systems,the WIII range is not very wide, much less than the current case wherethe minimum γ is 0.01 mN/m. It must be said also that in practice,with a lower tension minimum, it could be much wider, with a quitedifferent formulation for the minimum stability. In other words, ina three-phase emulsion, the excess water could be separated fasterthan the excess oil or the contrary, and this is why both stabilitycurves rise again after passing by a minimum somewhere inside theWIII zone.It is interesting to try to understand why the emulsionstabilityis always much lower in the WIII zone, whatever the case. The followingdiscussion is to explain that this is due to the bicontinuous structureof the middle phase microemulsion M, i.e., changes at the boundarybetween two and three-phase formulation.The stirring can be carried out with the WIII caseby taking onlythe excess oil phase and the M phase, so there is always an excessoil phase with practically no surfactant  and anaqueous phase that contains most of the surfactant. In the WI case,the water phase contains solubilized oil inside swollen micelles,and in the WIII case, higher solubilization happens in some structures,such as elongated micelles or more complex aggregates.As indicatedbefore, in the WIII range the volume of the middlephase is much less than in the surfactant containing water in thevery close WI case, with the same amount of surfactant. This meansthat the surfactant concentration in the middle phase M is much higherthan in the water phase in WI, typically 5 times in the present case.This occurrence produces more micelles but also allows the micellesto touch and probably to form other structures as elongated cylinderor “worm-like micelles” by percolation or fusioning.It is logically expected that at higher surfactant concentration,there will be more micelles and thus more light scattering, but theevidence is the opposite, as already seen in The fact is that in the WIII case, theinterfacial tension is lowerthan in the WI case and this also favors the elongation, since therelated energy term, i.e., the product of the tension by the area(γA), is reduced.Another interesting note is that witha bicontinuous structureshape in the film structure, even temporary, some short bypass canbe readily available, as seen in the right figure. Thus, coalescencebecomes instantaneous because of the difference in pressure betweenthe drops of different sizes. The amount of bypass probably dependson the exact position in the WIII zone, and thus justifies the minimumof both emulsion (O/M or W/M) cases slightly displacing one from theother as seen in R3 if it were a sphere. In contrast,the surface area depends only on the second power R2 of the globule size and on the thickness of the surfactantlayer L, i.e., a characteristic length like the surfactantextension that varies with the tail. Comparing this structure at differentsizes, the relation between the unit volume and unit surface is thesame, but if the surface is covered with a surfactant of characteristiclength L, which is the same in both globule sizes,the solubilization is not the same but depends on the size of theunit globule, as is evident with a structure made by cubes, cylinders,or spheres.1 and C2 principalcurvatures in the center drawing produces a higher solubilizationperformance SP and as well has a lower interfacial tension at optimumformulation as discussed elsewhere.78 Thismeans that the mean curvature is not a unique criterion to characterizethe situation, at optimum formulation when it is zero in all cases,whatever the surfactant, oil, water, and temperature values. It willbe the same with varying the globular sizes with a distribution ofdomain shape and size.Consequently, even with the same structure witha zero main curvature,the bigger size unity with lower C105 is not a surfactant characteristicat all, and the performance index PERFIND is probably more useful104 to make comparisons. Moreover, it is not acurvature nor a microcurvature either because such a concept requiresan oil/water interface or at least a solvent to dilute a surfactantas micelles or other aggregates, and the drops or micelle size dependson other parameters than the surfactant descriptor, in particularon the temperature, and water salinity including different ions.111Thus, the surfactant characteristic curvaturename CC proposedsome time ago112This last sectionis dedicated to propose a 4-dimensional (4D)spatiotemporal model of SOW simple systems at or close to optimumformulation according to the information available. This model willmake it relatively easy to explain in tutorial activities withoutthe usual puzzling confusions, as it is found in many detailed reviews,even recent ones with a lack of clarity in the microemulsion and curvatureterminology.22 times per second. In accordance with the experimental data followingthe small particles displacement by microscope, the average Brownianmotion is arbitrary and quite reduced in energy, thus likely to havean effect only at the molecular level, like spherical micelles orother surfactant aggregate structures. It means that it happens atthe scale of a very few nanometers, not at the usual macro-emulsiondrop size, which is typically millions of times bigger in volume ormass. Consequently, with a very high number of Brownian bumps, theactual result will be an average effect in time and in space of changesat the 1–10 nm scale.The model consistsin using, as the only mechanical energy generation,the Brownian motion thermal fluctuations, i.e. the bumping of thesurfactant structures by water or oil molecules about 1085 or incomplete, with no clear understanding on how to accountfor the curvature in the opened or connected part. Consequently, themicrocurvature can become positive or negative from place to place,zero if no separation surface, and during a very short time. Bothkinds of micelles at the same time, as proposed in Acosta’smodel,105 are not possible because bothexternal phases would be required. Therefore, in this case, it isthe surfactant film located at the oil–water limit that ispractically the external phase. As has been noted previously, thestructures can be elongated, in particular because of the low tensionclose to optimum, and open in a percolated worm type of associationby partial fusion of neighboring micelles.113The series of pictures in As a consequence, making a difference with the names and phenomenahappening at the different size levels is not only logical but alsonecessary to reduce the confusion.16 Otherresearchers in France have published interesting data.115For conventional emulsions,say with a radius of about 10 μm(or in the extended 1–100 μm range), drops are producedfrom an equilibrated SOW system by mechanical stirring, resultingin a strong light scattering as in the whitish milk. When the relativeaffinity of the surfactant for the oil and water is changed by a formulationor WOR variation  according to the Winsor multivariable concept, the emulsion(kept stirred) becomes inverted as was corroborated by the PIT namegiven by Shinoda group in Japan.117The supposed intermediate complex situation between the WIandWII cases, more or less understood as a very unstable mixture of theO/W and W/O emulsions, has been described by a catastrophe theoryoccurrence with a so-called “butterfly” manifold, withdouble cusp bifurcation, as explained in detail elsewhere.Gabcd(x) = x6 + ax4 + bx3+ cx2 + dx). It has up tothree minima, according to the ball in the hole analogy in the rightplot G(x) graphs and thus with thepossibility of up to 3 phase behavior. This G expressionhas 4 independent coefficients a, b, c, and d, where the “a” negative coefficient results in a double cuspindicated in the c-d map in theleft plot, similar to a Winsor triangle diagram.116 The effect of “b” is theequivalent to the generalized formulation, including T and P . “c” is equivalent to the surfactant concentrationand d to the water–oil ratio.Phase inversion of (macro)emulsion, like Shinoda’sPIT process,are catastrophe theory changes with time, i.e., dynamic phenomenawith high energy by stirring .As far as the phase behavior is concerned, it is an equilibrium situationwith no time effect . Itdoes not require external energy, i.e., no stirring with the exceptionof Brownian motion, i.e., a very low energy input that often requirestime to reach equilibrium, unless the formulation is at optimum, i.e.,with a very low interfacial tension, even a zero value.119 Exceptional hysteresiscan take place for a formulation change,120 probably because of delay in equilibration.121 Catastrophic phase inversion is also used to produce specificsolutions, in particular for viscous oil phases.122Thecatastrophe theory model predicted a possible hysteresis forthe inversion due to a change in WOR far from WOR = 1, as it is happeningin practice.C1 and C2 in a splay saddlestructure, which is a very different situation from micelles dispersionhappening away from optimum. Also, for a microemulsion to happen,the surfactant concentration must be quite large to get a single phase,whatever the complex structure. It is much higher than the typicalconcentration of less than 1%, usually used to get a macroemulsionfor many applications.For the microemulsion misleading name case, differentsituationshappen, and the term microcurvature will be logically used to avoidconfusion. The microcurvature is justified by the close to zero meancurvature of the separation surface. However, it is attained as thedifference between two very high principal curvatures 123 i.e., very small-sizeemulsions with interface and instability, it is better to keep themas normal emulsions according to their properties even if the “nano”part is not really appropriate because their droplets are, in general,larger than 50–100 nm,124 i.e.,larger than the size of a microemulsion domain, which is confusingsince nanometer means 10–9 m and micrometer 10–6 m.125For nanoemulsions,This review presents arguments sustainingthat what is called amicroemulsion is not a true emulsion and that the microcurvature isnot the same as the usual curvature concept in ordinary (macro)emulsions.Associating the term microcurvature with microemulsions may help toclarify the distinction or may create more confusion if this review’scomments are not properly understood.A microemulsion does notcontains drops but rather surfactant aggregationstructures with surfactant-oil-water wedge elements at the molecularlevel, such as micelles, liquid crystal, or more complex arrangements.Unlike macroemulsions, a microemulsion is a single phase and has nooil–water interface, no pressure difference inside and outsidethe structures, and is stable over time, not only because of the absenceof gravity effect but also because of some kind of mean value withlocation and time fluctuations. At and close to the so-called optimumformulation, it is bicontinuous and has no internal nor external phase,making it distinct from an emulsion, which is a dispersion of liquiddrops in another liquid external phase.The surface limit betweenoil and water domains in a microemulsionwas said to be a surfactant-rich monolayer or bilayer with a closeto zero curvature, i.e., a flat shapelike structure as in some liquidcrystals. It was proposed that diluting flat liquid crystals can providea liquid dissolution. i.e., a single phase with dispersed objectshaving a zero curvature that can be attained with a shape like a saddlewith two principal curvatures, which have different signs, and whosesum is zero. This is a puzzling manipulation of concepts to determinedomains similar to almost spherical drops or micelles. According tothe current discussions, the domains are of unknown shape, highlyvariable from place to place at a given time, and along the time ata given place. Thus, the overall microcurvature is a mean or averagethat could be measured, maybe with a preference slightly positiveor slightly negative, even if it is a difference between two veryhigh principal curvatures like in micelle and inverse micelle caseswith a small radius.Using the term “microcurvature”for microemulsionsystems could be a way to understand the differences and reduce confusion.Furthermore, a proper use of the wedge theory and packing parameterwith fluctuations when the interfacial tension is very low (at theoptimum) will allow one to explain that Brownian motion is enoughto provide the necessary fluctuations to have a stable single phaseaverage.


Definitions are important in healthcare. Unfortunately, problems can be found withall existing definitions of manipulation.This paper derives a set of eligibility criteria from prior definitions of manipulation to inform what should (and should not) be incorporated within a valid definition. These criteria were then used to select components from currently available empirical data to create a new definition.Separation (gapping) of opposing articular surfaces of a synovial joint, caused by a force applied perpendicularly to those articular surfaces, that results in cavitation within the synovial fluid of that joint.” The corresponding definition for the mechanical response of a manipulation is: “Separation (gapping) of opposing articular surfaces of a synovial joint that results in cavitation within the synovial fluid of that joint.” In turn, the action of a manipulation can be defined as: “A force applied perpendicularly to the articular surfaces.”The resulting definition of manipulation is: “We believe these definitions to be valid , complete , minimally sufficient , and robust (able to withstand important limitations embodied within sensible eligibility criteria). It is hoped that the simplicity and clarity of these definitions, and the transparency of their formation, will encourage their wide adoption in clinical, research, educational and professional settings. Definitions are important in healthcare. Amongst other things, they facilitate diagnosis , 2, consIn our 2010 paper [any synovial joint in the body. In this regard, it is reassuring that these necessary features fit neatly into a causal pathway without any obvious gaps . Equally important, surplus or redundant components should be excluded. To begin this process, one can identify categories of components from previous definitions Table  and thenalways occur when the defined event occurs. A corollary of this is that characteristics that occur some of the time  cannot be considered defining attributes. An obvious example for manipulation is the magnitude of applied force over time, and the resulting accelerations and velocities of motion. Four force-time phases have been identified as typically occurring during manipulation of spinal joints [orientation (or wind-up) phase; the preload phase; the thrust (or impulse) phase; and the resolution phase. Notably, not all of these phases occur during spinal manipulation, even when all of the events depicted in Fig. Components of an intensional definition must be consistent; they must l joints –26: the the intent to restore optimal motion, function, and/or to reduce pain” [Some previous definitions of manipulation , 16 havece pain” –32. It iFor any intervention to have therapeutic potential, it must be able to act upon a biological target . The bioaction (that which the practitioner does to the recipient) and the mechanical response (that which occurs within the recipient) [Pharmacodynamics is essentially ‘what the drug does to the body’, which will commence at the biological target. Accordingly, the dynamics of manipulation  will begin with events occurring at a synovial joint. Hence, a definition of manipulation should certainly incorporate the events of the mechanical response, all of which occur within the synovial joint (Table The necessary features listed in Table cipient) . Anothernt Table .When applied to a class of phenomena, an intensional definition must apply fully to all members of the class . If a symechanical response will be those consistently observed across multiple different synovial joints, both in the periphery and within the spine. Indeed, of the synovial joints to have been studied, the metacarpophalangeal (MCP) joint is by far the most common. Notably, the highest quality basic science research on joint manipulation originated not from clinicians interested in its therapeutic potential, but bioengineers interested in the phenomena of MCP joint ‘cracking’ [In turn, the necessary characteristics of the racking’ , 37. Thiracking’ , 24, 43,racking’ .action. As can be seen in Table that which the practitioner does to the recipient in definitions of manipulation. However, it could be argued that the components of the mechanical response depicted in Fig. that which occurs within the recipient) could alone sufficiently define a manipulation, and that those of the action would therefore be redundant in any such definition. Indeed, Newton’s first law of motion already requires that a (component of) applied force must be perpendicular to the articular surfaces of a joint if they are to separate. However, the converse is also true: it would be necessary to include components of the action if the components of the mechanical response were alone insufficient to define manipulation.An intervention, whether in healthcare or elsewhere, suggests the occurrence of some form of mechanical response may be achievable outside of the order in which they are depicted in Fig. mechanical response depicted in Fig. action into a definition of manipulation, the causal sequence depicted in Fig. action in definitions of manipulation.It turns out that the elements of the action that initiates the intervention. Examples include, “A passive, manual manoeuvre …” [A manual procedure …” [High velocity, low amplitude passive movements …” [A passive, high velocity, low amplitude thrust …” [action is problematic because its elements  …”. However, a safer and more future-proof solution is to altogether avoid including the origins of the action in definitions of manipulation.Separate from intention, several prior definitions of manipulation have – at their root – explicitly described (and thereby limited) the origin of the euvre …” , “A manuedure …” , “High vments …” , “A passhrust …” . As can transient sensory afferent input” [supraspinal mechanisms including expectation of benefit” [mechanical response of a manipulation that might appear downstream from the biological target of the synovial joint  will act through physiological pathways that are not exclusive to manipulation and could feasibly be produced in some alternative way . Hence, these downstream physiological pathways can be shared by other interventions and are therefore surplus to the essential characteristics required to define manipulation. Consequently, they must fall outside of the scope of a definition of manipulation.Previous definitions of manipulation have incorporated putative downstream consequences; for example, “t input”  and “supbenefit” . The proDownstream consequences of manipulation are also dependent upon the person being alive, and all that is bestowed by this. Yet, a manipulation performed on a cadaver must still constitute a manipulation if all necessary components are deemed to occur. Indeed, multiple important cadaveric studies of manipulation , 47–55 wnecessary conditions for the intervention. As such, the intervention itself must be defined by such a state. Notable by its absence in previous definitions of manipulation is the lack of reference to a specific disease or pathological state; although one definition [delivered at the end of the restricted physiologic limit of a joint’s range of motion.”Some healthcare interventions, such as the extraction of a splinter or the relocation of a dislocated bone, can only be performed if a certain disease or pathological state is present. These are known as finition  did impoindications for its use. Conversely, if a specific disease or pathological state poses a risk for an intervention, these conditions are known as contra-indications. Incorporating indications and contra-indications into definitions of interventions can be problematic because they can be different for individual patients. For example, if spinal pain was incorporated into a definition of manipulation, how does one then deal with spinal pain that is caused by spinal malignancy, osteoporotic fractures, tuberculosis, or a cervical artery dissection? Such a definition would become extensional, requiring exhaustive lists that would require endless modification and caveats over time as new data arose. By instead using an intensional definition, the appropriateness of each incorporated necessary component of the intervention can be judged for every individual patient, and the need for such a list is avoided.If an intervention is considered potentially therapeutic for a specific disease or pathological state, these conditions are considered Since manipulation can be performed upon either a healthy or an unhealthy synovial joint , it is an intervention whose occurrence can be independent of health status, the presence or absence of disease, and pathological states. Hence, it should also be defined independently of such conditions.Previous definitions of manipulation have incorporated beneficial clinical outcomes, such as pain relief , 19. Howmechanical response of a manipulation must be separated out from the clinical outcome. In their discussion of definitions, McCarthy and colleagues [action of the clinician) led to a mechanical response . In turn, this action and consequential mechanical response can purportedly lead to canalith repositioning, but this mechanistic pathway is only available if canalith malposition is a pre-existing pathological state within the recipient. In other words, both gravitational forces and canalith malposition are necessary conditions for this mechanistic pathway to exist. Finally, the recipient may or may not result in a beneficial clinical outcome (and this may or may not be related to the above mechanistic pathway). From randomised controlled trials of Epley manoeuvres for the canonical condition of benign paroxysmal positional vertigo [In particular, the lleagues  used the vertigo , it is caction and mechanical response from which they would originate.A useful definition of manipulation must fit within a wider taxonomy of physical interventions, and in particular those within the domain of manual therapy. Within such a taxonomy, different interventions should be distinguishable and mutually exclusive of one another by readily measurable factors. By historical convention  these factors should be mechanical in nature. By contrast, the clinical outcomes of such physical interventions appear to be very similar , which iAs we stated in 2010 [Collectively, the eligibility criteria set out above and summarised in Table thrust, for example, is used in the colloquial sense and is therefore inappropriate for a formal definition [Several existing definitions  originate from the influential but ultimately flawed model of Sandoz [As has been described in detail elsewhere , 43, 44,f Sandoz . Notablyf Sandoz . Importap) during its rotational motion around a static centre of rotation (c). As guided by the partitioned diagrams, the relationship between the centre of rotation (c) and the fixed point (p) dictate both the correct location and extent of the para-physiological space [para-physiological space resides upon the upper border of the arc depicting the rotational range of motion of the joint. While the joint surfaces are in contact, the para-physiological space has no area in this two-dimensional representation . The space is therefore a potential space, akin to that of the pleura, only becoming real and apparent when the surfaces separate [As per Sandoz’s original model , Fig. 2 al space , 44. Unlal space , the parOnce familiarised with the corrected model of manipulation in Fig. Given the eligibility criteria and corrected model presented above, and the individual components from Table Definition 1:Separation (gapping) of opposing articular surfaces of a synovial joint, caused by a force applied perpendicularly to those articular surfaces, that results in cavitation within the synovial fluid of that joint.mechanical response can be constructed by simply removing the text between the commas in Definition 1:In turn, a definition for the Definition 2:Separation (gapping) of opposing articular surfaces of a synovial joint that results in cavitation within the synovial fluid of that joint.action can be defined using the text between the commas in Definition 1:Lastly, the Definition 3:A force applied perpendicularly to the articular surfaces.all necessary components of manipulation [mechanical response (Definition 2) and action (Definition 3) are not required for Definition 1 to stand alone but should be useful when practising, teaching, researching, and evaluating manipulation.We believe that Definition 1 encompasses pulation , as listaction and mechanical response should be included within a definition of manipulation. In line with our eligibility criteria, we have placed no restrictions on the origins of the force comprising the action (Definition 3); just that its line of action (or at least a component of it) is perpendicular to the articular surfaces of the joint [A manual procedure that involves …” or “A passive, manual manoeuvre during which …”.We argued above that both he joint . Hence, caused by …” and “results in …” within Definition 1 to ensure the sequence of events described in Fig. mechanical response (Definition 2) deliberately describes a causal pathway that occurs within the recipient, beginning with the separation of articular surfaces of a joint, which then results in the cavitation event within the synovial fluid of that joint; a sequence of events that has been demonstrated multiple times in mutually supporting independent studies [mechanical response (Definition 2) mentions nothing of low-amplitude displacement, nor any criterion relating to ranges of motion, physiological limits, anatomical limits, boundaries, barriers, or tissue damage, which we believe to be surplus to requirements for a definition, even though some of these concepts were retained in the corrected model of manipulation  within Definition 1 should serve as a useful guide for clinicians in terms of what is – and what is not – required to create the mechanical response during the delivery of manipulation. Indeed, notably absent from the action (Definition 3) is any mention of high-velocity motion, which is alluded to in nearly all previous definitions of manipulation.In addition to the earlier arguments put forward, the explicit inclusion of the not constitute a manipulation but could instead be described as an ‘attempted’ manipulation. If all necessary components apart from cavitation occur, this would constitute ‘joint distraction’ , all components of which are measurable and verifiable [Importantly, although downstream effects that might be specific to manipulation are not incorporated within the above definitions, such effects should be entirely attributable to the rifiable , 28, 38.We are aware that some might be uncertain as to how these new definitions could and should be used. We believe that these new definitions will allow manipulation to be more easily taught to students, better studied by researchers, more fairly evaluated by guideline panellists, and that clinicians will be better able to decide upon indications and contra-indications for individual patients.action and mechanical response are also provided. It is hoped that the simplicity and clarity of these definitions, and the transparency of their formation, will encourage their wide adoption in clinical, research, educational and professional settings.This paper presents a new definition of manipulation, which we believe to be valid , complete , minimally sufficient , and robust (able to withstand important limitations embodied within sensible eligibility criteria). Corresponding definitions for the