“Knowledge is justified, true, and undefeated belief.”
That deceptively simple definition of knowledge has endured for centuries. To know something, we must believe it sincerely, our belief must correspond with reality, and it must be justified by reasons or evidence strong enough to resist defeat. The moment counter-evidence appears, knowledge demands revision.
We can hold a belief tightly, love it, even build our world around it—but if reality contradicts it, we must decide: cling to familiarity, or surrender to truth.
In philosophy, that surrender is the moment of knowing.
We might begin with frogs.
Dissect a thousand frogs and find that every one is green; you may declare, with confidence, that all frogs are green. For a time, it feels like knowledge. Then, one day, a red frog hops into view. Instantly, your certainty collapses. The rule must change: most frogs are green.
Knowledge adapts, or it dies.
So too with gender. Many people claim to know that women are born with vaginas and men with penises as if anatomy were the essence of identity. Yet the world presents its red frogs in abundance: intersex people, trans women, trans men, non-binary lives. Once these exist, as they always have, the old definition can no longer stand.
Philosophy calls this process defeasibility: the requirement that knowledge be able to survive defeat. A claim that cannot change is not knowledge; it is dogma.
Dogma comforts us by freezing the world. Knowledge humbles us by insisting the world moves.
And if we follow that humility to its end, we find that trans existence does not challenge knowledge it perfects it.
The Shape of Knowing
Epistemology is, at heart, a discipline of honesty. It asks: what entitles us to say we know anything at all?
Belief alone isn’t enough. I can believe the sky is green. Truth alone isn’t enough. I can stumble on a correct guess by luck. Justification without openness is brittle. But when belief, truth, and justification align, and when that belief remains undefeated by contrary evidence - we reach something solid.
Trans existence meets that test.
The belief that trans women are women and trans men are men is justified philosophically, biologically, socially, and ethically. It corresponds with observable reality. And, crucially, it remains undefeated by evidence; every attempt to disprove it collapses under scrutiny.
Beyond Tradition
Human beings are addicted to certainty. We cling to simple binaries because complexity is frightening. Yet philosophy teaches that certainty is often ignorance dressed up as truth.
Judith Butler warned decades ago that “gender proves to be performance—constituting the identity it is purported to be” (Butler 1990, 25). Identity is not a fossilized category but an ongoing act, performed through speech, gesture, and social relation.
Long before Butler, Simone de Beauvoir wrote, “One is not born, but rather becomes, a woman” (Beauvoir 1949, 267). She saw that gender arises through a process of becoming, not a static possession of flesh.
And philosopher Talia Mae Bettcher built on that lineage, arguing that trans people have first-person authority over their own gender (Bettcher 2009, 110). Knowledge begins with the testimony of those who live it. To deny that authority is not skepticism. It is epistemic injustice.
Tradition, however venerable, is not justification. It describes how people once believed, not necessarily what is true. When new realities contradict old definitions, philosophy instructs us to revise.
Biology in Motion
Those who protest that “biology proves sex is binary” mistake a field for a verdict. Biology is not a court; it is the study of life’s variation.
Living systems change. Chromosomes, hormones, and anatomy form overlapping spectra. Intersex variations alone prove that binary categories are descriptive conveniences, not absolute boundaries.
Modern endocrinology shows how powerfully adult bodies respond to hormonal environments. Within a year of feminizing hormone therapy, trans women experience measurable shifts in fat distribution, muscle mass, and hematologic markers changes that align closely with cis female ranges (Cheung et al. 2023; Harper et al. 2021). The body is not fixed; it is responsive.
The brain, too, participates in this adaptation. Longitudinal MRI studies demonstrate hormone-linked remodeling of gray matter and microstructure in adults undergoing gender-affirming therapy (Seiger et al. 2016; Kiyar et al. 2022; Handschuh et al. 2024). Biology, far from refuting trans identity, records it.
Clinical consensus follows. The Endocrine Society’s guidelines and the WPATH Standards of Care, Version 8 recognize gender-affirming hormone therapy (GAHT) as evidence-based medicine that aligns secondary sex traits with affirmed gender and correlates with improved mental-health outcomes (Coleman et al. 2022).
In short: biology supports transition because biology describes change.
The Body and the Social
Humans are not merely biological organisms; we are social ones. The environments we inhabit - our communities, stresses, and recognitions, shape our physiology. Social affirmation lowers cortisol, improves immune response, and rewires neural pathways. Rejection and stigma do the opposite.
Jack Halberstam offers a metaphor that captures this reciprocity: “Gender might be thought of more as a climate or ecosystem and less as an identity or discrete bodily location” (Halberstam 2018, xiv). To be recognized as a woman or a man is to live within a particular climate of expectations and relations. Over time, that climate becomes embodied.
Social womanhood and biological womanhood are thus entangled processes. To live as a woman socially, hormonally, experientially, is to develop within the same adaptive system that defines womanhood itself.
Trans women, accordingly, are not exceptions to a rule but expansions of it. Their bodies and lives reveal what biology actually does: it listens, it adjusts, it learns.
Living Evidence
Knowledge is empirical. It demands evidence, and trans existence offers it in abundance.
Every clinical study that tracks gender-affirming care shows the same pattern: depression and anxiety decrease, life satisfaction increases, suicidal ideation drops (Poteat et al. 2023). These outcomes are not political. They are biological and measurable.
To insist that such lives are “unnatural” is to prefer ideology over data. The claim that gender identity is determined solely by reproductive anatomy is defeated by observation. It no longer qualifies as knowledge.
Philosophy requires we accept defeat gracefully.
The Moral Weight of Knowing
Knowing is never neutral. Once evidence shows that a belief harms people when held falsely, persisting in that belief becomes a moral failure.
The conviction that trans women are not “real” women, or that trans men are deluded, is not only incorrect. It is cruel. It translates directly into violence, exclusion, and policy that withholds care. The WPATH Standards of Care explicitly warn that denying medically indicated treatment can have iatrogenic effects, meaning harm caused by the refusal itself (Coleman et al. 2022, S24).
In epistemology, we call this epistemic responsibility: the duty to update beliefs in proportion to evidence. In ethics, we call it compassion. They are not different virtues.
Beyond the Split of Body and Mind
For centuries, Western thought separated mind and body, nature and culture, male and female. But the seams are showing.
Social life has biological consequences; biology is the memory of social life. To insist they are separate is to miss how living beings actually function.
A trans woman who transitions socially and medically inhabits the same ecological niche that cis women do. Her endocrine profile, muscle composition, and neural activity adapt to estrogenic environments; her social experiences, both affirming and hostile, mold her physiology through stress and resilience. She becomes biologically and socially a woman.
To deny her womanhood because of an origin story is like denying a butterfly’s membership in “insect” because it no longer resembles a caterpillar. Biology is not essence; it is evolution.
The Lived Philosophy
Philosophy, when honest, bends toward those who live what it theorizes.
Susan Stryker wrote of being seen as monstrous because of embodiment: “Like the monster, I am too often perceived as less than fully human due to the means of my embodiment” (Stryker 1994, 240). Yet in the same essay she claims that monstrosity as liberation, declaring, “I can embrace language with a vengeance to rename myself” (ibid., 247).
Julia Serano reminds us that hostility toward trans women often hides hostility toward femininity itself: “The real ruse is by those who place inferior meanings onto femininity” (Serano 2007, 16).
Paul B. Preciado reframes hormones not as medical corrections but as political tools, writing that “the body could never be a material given before linguistic or political action” (Preciado 2013, 41).
And Bettcher grounds the entire conversation in self-knowledge: “trans people have first-person authority.” That sentence is both epistemology and ethics—a reminder that knowledge begins with listening.
These thinkers do not speak in unison, but together they form a choir of understanding: bodies are dynamic, truth is relational, and to know is to respect becoming.
The Unfolding Truth
If knowledge is justified, true, and undefeated belief, then trans reality qualifies on all counts.
It is justified by philosophical reasoning, by medical observation, by lived testimony.
It is true because it corresponds to the world as it is: complex, diverse, mutable.
And it is undefeated, for every attempt to disprove it fails against evidence.
Clinging to outdated definitions “women are born with vaginas,” “men produce sperm,” is not knowledge. It is nostalgia dressed as certainty. The red frog has been found; the universe asks us to learn.
To know ourselves anew is not to erase what came before but to deepen it, and to replace brittle binaries with living categories that breathe.
To Accept Is to Know
We have always revised our understanding of what it means to be human. We once believed Earth stood still. We once believed disease was punishment. We once believed gender immutable. Each belief fell when the evidence rose.
Trans people are not anomalies in this story; we are its continuation. Our lives expand humanity’s vocabulary for itself.
As Halberstam suggests, think of gender as climate. As Butler reminds, it is something we do. As Bettcher insists, self-knowledge is data. As Serano defends, femininity is not weakness but complexity. As Stryker declares, the monster was never the threat. It was the mirror.
Knowledge that excludes reality is not knowledge at all.
To deny the truth of trans existence is to surrender truth itself.
To accept it is to know.
References
Beauvoir, Simone de. 1949. Le Deuxième Sexe. Paris: Gallimard.
Bettcher, Talia Mae. 2009. “Trans Identities and First-Person Authority.” Hypatia 24 (3): 98–118.
Butler, Judith. 1990. Gender Trouble: Feminism and the Subversion of Identity. New York: Routledge.
Cheung, A. S., et al. 2023. “Changes in Body Composition in Transgender Individuals on GAHT.” Journal of Clinical Endocrinology & Metabolism.
Coleman, Eli, et al. 2022. “Standards of Care for the Health of Transgender and Gender Diverse People, Version 8.” International Journal of Transgender Health 23 (sup 1): S1–S259. https://doi.org/10.1080/26895269.2022.2100644
Halberstam, Jack. 2018. Trans: A Quick and Quirky Account of Gender Variability. Berkeley: University of California Press.
Handschuh, P., et al. 2024. “Brain Structural Changes After Hormone Therapy in Transgender Adults.” NeuroImage Clinical 34: 103310.
Harper, J., et al. 2021. “How Does Hormone Therapy Affect Strength and Endurance in Transgender People?” Sports Medicine 51 (11): 2215–2230.
Kiyar, S., et al. 2022. “Hormone-Driven Brain Plasticity in Transgender Individuals.” Cerebral Cortex 32 (5): 1012–1024.
Poteat, T., et al. 2023. “Hormone Therapy, Mental Health, and Quality of Life in Transgender Adults: A Systematic Review.” JAMA 330 (6): 555–564.
Preciado, Paul B. 2013. Testo Junkie: Sex, Drugs, and Biopolitics in the Pharmacopornographic Era. New York: Feminist Press.
Seiger, R., et al. 2016. “Cortical Thickness Changes After Cross-Sex Hormone Therapy.” Brain Research 1644: 132–142.
Serano, Julia. 2007. Whipping Girl: A Transsexual Woman on Sexism and the Scapegoating of Femininity. Berkeley: Seal Press.
Stryker, Susan. 1994. “My Words to Victor Frankenstein Above the Village of Chamounix.” GLQ 1 (3): 237–254.