Abstract

This commentary proposes the semi-permeable membrane as a conceptual framework for reconsidering medical classification and knowledge production. Drawing on Hacking's observation that "people spontaneously come to fit their categories" and Mol's embodied epistemology, I examine how diagnostic frameworks simultaneously constitute and are constituted by the bodies they classify. Medical categories are not neutral descriptors but transformative forces that shape clinical reality—selectively permitting certain understandings while excluding others. Through interdisciplinary engagement with disability justice scholarship and critical theory, I demonstrate how this biological metaphor illuminates the politics of medical knowledge: what passes through institutional boundaries, what remains excluded, and how these determinations reflect power relations. For clinicians and educators, this perspective invites reimagining clinical encounters as sites of "reciprocal capture" where neither biomedical frameworks nor patient narratives subordinate the other. As I prepare to enter medical training, I argue that selective permeability offers both analytical lens and ethical imperative—maintaining necessary diagnostic boundaries while acknowledging their contingency and remaining open to transformation through encounter. This reconceptualization has implications for how we teach, practice, and ultimately understand the relationship between medical categories and human suffering.

Keywords:  medical epistemology, categorization, embodiment, semi-permeable membrane, medical education

"People spontaneously come to fit their categories," writes Ian Hacking, capturing how diagnostic classifications are not merely descriptive but transformative forces that reshape both the subjects classified and those who deploy these classifications (Hacking 1999, 161). This dialectical relationship between knower and known parallels Annemarie Mol's observation that "neither tightly closed off, nor completely open, an eater has semi-permeable boundaries" (Mol 2008, 30). As I prepare to enter medical school, I find myself contemplating the productive power of medical taxonomies through this integrated lens: How categories and bodies constitute each other through processes of selective exchange, much like a semi-permeable membrane. This biological metaphor offers a critical perspective on how medical knowledge is simultaneously constructed, maintained, and transformed through ongoing negotiations of boundaries.

Hacking's insight that multiple personality disorder "was invented around 1875" rather than discovered challenges traditional understandings of medicine as the gradual uncovering of biological reality (Hacking 1999, 162). His diction choice, "invented" rather than "discovered," is deliberately jarring. Medical categories operate not just descriptively but performatively, bringing into being the phenomena they claim merely to identify. The historical contingency of diagnostic frameworks destabilizes the traditional understanding of medicine, which presents categories as the gradual uncovering of biological reality.

This perspective parallels critiques of knowledge appropriation in scientific practice. As Liboiron notes, "Imperialism and colonialism both involve the scientific appropriation of local and Indigenous knowledges, eaten up and digested to create dominant scientific knowledge" (Liboiron 2017, 53). The pharmaceutical industry reinforces hierarchical distinctions between "traditional healing" and "scientific medicine" when they extract active compounds from traditional medicines without acknowledging their origins. When Hacking observes that "counting generated its own subdivisions and rearrangements," he identifies the technical apparatus of classification that actively shapes the phenomena being classified (Hacking 1999, 161). If medical categories are not neutral descriptors but active forces that shape reality, we need metaphors that capture this dynamic interplay between knowledge and embodiment.

In biology, the semi-permeable membrane is a critical boundary between the cell and its environment, selectively allowing certain substances to pass while maintaining cellular integrity. Just as Hacking's categories transform their subjects through classification, Mol's theory of eating and incorporation suggests that embodied knowledge transforms both knower and known. Indeed, "philosophical theories incorporate metaphors," and the semi-permeable membrane is no exception (Mol 2008, 34). As Mol writes, "here is the apple, there am I. But a little later (bite, chew, swallow) I have become (made out of) apple; while the apple is (a part of) me" (Mol 2008, 30). She further argues, "Texts may tell about an object, but they come from somewhere, too. They incorporate an author" (Mol 2008, 32). This embodied epistemology provides a conceptual bridge to Hacking's insight that categories transform their subjects—both approaches recognize that knowledge practices actively constitute reality rather than passively describing it.

This embodied epistemology mirrors how cellular membranes both maintain identity and transform through selective exchange. The semi-permeable membrane also reflects how knowledge is filtered through institutional power structures that determine which ideas circulate and which are excluded from discourse. Not all identities can penetrate institutional boundaries, and permeability often reacts strategically to perceived threats. When environments become inhospitable, adaptation emerges through what Wong calls "crip technoscience," a concept from disability justice that frames bodily adaptation as strength rather than defect (Wong 2019, 3). This adaptive capacity of bodies offers important insights for how we might reconceptualize clinical encounters beyond rigid binaries.

Diet culture exemplifies how biological metaphors become sites of ideological enforcement. Consider an eating subject persuaded by fad diets to eliminate all carbohydrates. Obesity "is a problem," but since when were "carbs = bad / no carbs = good?" (Wong 2019, 4). This reduction parallels Wong's critique of "the simplistic binary of plastic = bad / compostable = good" (Wong 2019, 4). Such binaries obscure lived complexity, especially when framed as moral imperatives rather than metabolic functions.

Stripped of choice, preference, and agency, the carbohydrate-deprived body craves bread, chocolate, and ice cream. Without glucose, the "smaller and less accessible" (Wong 2019, 7) cell loses its "decision making, representation, and participation" in energy production (Wong 2019, 6). This metabolic metaphor is "about power: who knows best, who decides how change is made, who is centered in all these activities" (Wong 2019, 4).

Instead of discriminating substances based on abstract judgments, the semi-permeable membrane engages with contextual utility. This approach echoes Deborah Bird Rose's concept of "reciprocal capture," a relationship "in which neither entity transcends the other or forces the other to bow down" (Rose 2017, G51). When applied to clinical encounters, biomedical categories might engage with patients' lived experiences without subordinating them, opening space where "possibilities for new modes of existence emerge" (Rose 2017, G52). Such reconfigured clinical relationships inevitably raise questions about power, authority, and the politics of who determines what counts as medical knowledge.

Foucault's medical gaze goes beyond simply observing bodies; it constitutes them as objects of specific kinds of knowledge and intervention. In a sense, Hacking's idea of "making up people [is] intimately linked to control," for medical categories simultaneously enable care and constrain our perception of suffering (Hacking 1999, 164). Medical categorization can never be politically neutral. The DSM's revisions exemplify boundary work in action—when homosexuality was removed in 1973 or the recent addition of prolonged grief disorder, these decisions were not just clinical but contests over what counts as normal variation versus pathology. These negotiations introduce ethical and political determinations with profound consequences for how we understand ourselves and how institutions allocate resources.

Our bodies' multispecies entanglements reveal constant boundary negotiations that are neither wholly autonomous nor completely permeable. The processes of osmosis and facilitated diffusion exemplify "conceiving embodiment as never 'auto' nor 'immune' but a co-inhabitant ecology" (Briggs et al. 2024, 4). The semi-permeable membrane metaphor reveals that subjectivity is not a static possession but an ever-evolving process of negotiating necessary and provisional boundaries. Yet, this metaphor risks reducing conscious agency to automatic biological processes, overlooking how people actively reflect, resist, and reshape their boundaries beyond molecular logic. Nevertheless, this reconceptualization invites us to consider the operationalization of knowledge production, disability justice, and chronic illness communities within medical education and clinical practice.

For medical practitioners and educators, this perspective offers several concrete implications. First, it suggests that diagnostic interviews might be reconceptualized as sites of co-production rather than extraction—clinicians and patients collaboratively negotiating which aspects of experience are relevant, rather than imposing predetermined categories. Second, it calls for teaching medical trainees to recognize diagnostic frameworks as constructed tools rather than neutral descriptions. Third, it highlights the importance of interdisciplinary approaches to illness that acknowledge the multiple systems through which suffering is constituted and addressed.

As future healthcare providers, we must recognize that knowledge production inevitably involves inclusion, exclusion, visibility, and erasure. In medical categories, certain aspects of human suffering are acknowledged while others are inevitably obscured. However, recognizing this partiality does not mean abandoning categories altogether—diagnosis remains essential for addressing suffering—but adopting a more reflexive approach to classification.

Selective permeability is not merely a cellular property but a clinical and epistemic imperative that might transform doctor-patient relationships. Understanding the politics of knowledge does not diminish its utility but enhances our capacity to use it responsibly. As I transition into medicine, I hope to maintain this awareness of how categories simultaneously enable care and constrain our perception of suffering, seeking diagnostic frameworks that acknowledge their constructedness while still serving as tools for healing. Perhaps the most ethical medical practice is one that, like the semi-permeable membrane, maintains necessary boundaries while remaining open to transformation through encounter.

References

Bird Rose, Deborah. "Shimmer: When All You Love Is Being Trashed." In Arts of Living on a Damaged Planet, G51–63. Minneapolis: University of Minnesota Press, 2017.

Briggs, Charles, Sharon Daniel, Alexandra Juhasz, Pato Hebert, Tammy Ho, Rachel Lee, Cynthia Ling Lee, et al. "Introducing How We Make It: Disability Justice, Autoimmunity, Community, a Multimedia Project." Catalyst: Feminism, Theory, Technoscience 10, no. 1 (2024): 1-21.

Hacking, Ian. "Making Up People." In The Science Studies Reader, 161–71. London: Routledge, 1999.

Liboiron, Max. "Land, Nature, Resource, Property." In Pollution Is Colonialism, 39–79. Durham: Duke University Press, 2021.

Mol, Annemarie. "I Eat an Apple. On Theorizing Subjectivities." Subjectivity 22, no. 1 (2008): 28–37.

Wong, Alice. "The Rise and Fall of the Plastic Straw: Sucking in Crip Defiance." Catalyst: Feminism, Theory, Technoscience 5, no. 1 (2019): 1–12.