Being a twin can reveal that individuality is not always a sealed, self-contained property. In her 21 November 2023 Aeon essay, philosopher Helena de Bres argues that close twins may share parts of cognition, agency and identity while remaining two fully distinct people.
Her claim is philosophical rather than a finding that twins are literally one person. It asks a harder question: if another person reliably helps you remember, decide, act and understand who you are, where exactly does your individual self end?
The direct answer: individuality can be separate and shared
De Bres’s central proposal is that personhood can have degrees. A twin may be an individual with a private body, perspective and responsibilities, yet also participate in a shared mental and practical life with a sibling. The relationship does not erase either person. Instead, it shows that being a person may involve both separation and connection.
This challenges a familiar picture in which one person is completely contained inside one body and one brain. On that picture, anything outside the skin is merely an influence on the self. De Bres asks whether some relationships can become constitutive of what a person thinks, does and cares about. Her formulation is deliberately open-ended: “What if a person isn’t only something you are, but also something you do?”
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What Helena de Bres is arguing—and what she is not
De Bres is a philosophy professor at Wellesley College and the author of How to Be Multiple: The Philosophy of Twins (2023). The Aeon piece is a first-person philosophical argument shaped by her experience with her twin, Julia. Its autobiographical examples illustrate possibilities; they are not a survey of twins and should not be treated as representative evidence about every twin relationship.
The essay does not claim that twins communicate telepathically, possess one consciousness or have identical personalities. Nor does it say that a shared history creates one legal or moral subject. De Bres’s narrower thesis is that some close twins share personhood “to a significant degree” through three connected phenomena: shared cognition, plural agency and shared identity.
Why a body-to-person map is too simple
A bounded body does not settle who a person is
Everyday language encourages a one-body/one-person assumption: one envelope of skin appears to mark the boundary of one self. De Bres separates the biological material of a human organism from the organisation and capacities that matter for personhood. Having a body, or a particular set of genes, is relevant, but neither fact alone provides a complete theory of who someone is.
Chimerism helps expose the limitation. A chimera can have cell lines with different genetic profiles within one body. That biological complexity does not automatically make the individual two people. The example shows why DNA cannot, by itself, determine the number of persons present. Personhood depends on how capacities, perspectives, agency and relationships are organised, not simply on counting genetic patterns.
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Conjoined twins reverse the usual thought experiment
Conjoined twins provide a different challenge. Twins with two heads generally regard themselves as distinct people despite sharing a body. Their case makes it difficult to infer the number of persons directly from the number of bodies. Two subjects can inhabit one bodily structure, just as two separate bodies can become deeply integrated through a relationship.
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These cases are philosophical counterexamples, not evidence that every twin relationship has the same structure. Chimerism concerns the relation between cells and biological identity; conjoined twins concern the relation between a shared body and distinct subjects. De Bres uses each to unsettle a different assumption before turning to ordinary, non-conjoined twins.
Three ways close twins may share personhood
1. Shared cognition: thinking with another person
Close twins may divide and coordinate cognitive work. One remembers a detail that the other cannot retrieve; a question, phrase or gesture prompts a memory; together they reconstruct an event more accurately than either could alone. De Bres describes trusting Julia’s memories as part of their shared cognitive life rather than treating every recollection as an entirely private possession.
She connects this possibility to Andy Clark and David Chalmers’s 1998 “The Extended Mind,” which asks whether tools and environments can function as parts of a cognitive process, and to Daniel Wegner’s work on transactive memory, in which groups rely on knowledge about who can recall what. Applied to twins, these frameworks describe dependable social scaffolding: each person becomes a resource the other can consult and coordinate with.
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2. Plural agency: acting as a “we”
Agency is usually described in the singular: an individual forms an intention and performs an action. De Bres draws on philosopher Bennett Helm’s account of group agency to show how a “we” can also have concerns and commitments. People can care about a shared aim, endorse it together and treat the group’s success as part of what each person is doing.
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Her childhood collaborations with Julia supply an ordinary example. A joint project, scheme or decision can be planned through conversation and carried out by both partners, with neither contribution making sense in isolation from the other. The resulting action is not reducible to two unrelated acts, yet it does not require a mysterious third mind. It is a coordinated commitment sustained by the participants.
Plural agency does not mean that twins share every intention. One may refuse a plan, change her mind or pursue a private goal. Shared agency exists where commitments genuinely belong to the pair, in a particular situation or domain. The same pattern can appear in non-twin relationships, but the long duration and intensity of twin collaboration can make it especially visible.
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Identity includes more than a list of traits. It also includes the relationships and commitments through which a person understands her life. A deep twin bond can become part of each sibling’s self-conception: “we” may be a meaningful answer to questions about who they are, what they have accomplished and what matters to them.
De Bres calls this a possible form of shared identity while rejecting the claim that the twins are simply identical. Each sibling can have private memories, friendships and obligations that the other does not possess. Shared identity is therefore layered and selective. It may concern family history, a creative practice, a moral commitment or a style of responding to the world without covering every aspect of either life.
Three philosophical models side by side
The contrast is easiest to see as a set of dimensions rather than a choice between two all-or-nothing theories.
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| Question | Strictly bounded individual | Relational account in de Bres’s argument | What the twin examples show |
|---|---|---|---|
| Where does cognition occur? | Only inside one person’s brain; other people are external influences. | Reliable social scaffolding can become part of how remembering and problem-solving are carried out. | A twin pair may use one another’s memories and prompts as a stable cognitive resource. |
| Who can be an agent? | Only a single person can own an intention or action. | A group can form shared concerns, commitments and aims while its members retain private agency. | Twins can act as a “we” in particular projects without becoming one subject in every context. |
| How is identity bounded? | Identity is fixed inside the skin and remains conceptually separate from relationships. | Identity can be relational, domain-specific and change across time. | A twin relationship may become part of each sibling’s self-understanding without exhausting it. |
| What follows ethically? | Responsibilities belong only to separate individuals. | Shared commitments can create reasons to act together, alongside individual duties. | Closeness matters morally, but it does not transfer every obligation from one twin to the other. |
Shared personhood is dynamic, not permanent fusion
De Bres’s proposal allows people to move in and out of shared personhood. The degree of sharing can increase during a joint task, fall away when each person pursues separate work and change as the relationship develops. It can also vary by subject: two siblings may coordinate effortlessly about family memories while disagreeing about politics or maintaining entirely separate professional lives.
This temporal and domain-based view avoids two opposite mistakes. It does not reduce the relationship to a series of unrelated individual actions, but it also does not turn every shared experience into evidence of a single permanent self. “Shared” describes an activity or commitment that the people sustain together, not a cancellation of their boundaries.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.What the argument implies for responsibility and recognition
If personhood can be partly relational, then institutions and other people should be cautious about demanding a simple either/or answer. A twin may speak in the first-person plural about a decision and still expect to be addressed as an individual. Friends and family may recognise a powerful bond without assuming that one sibling knows every thought of the other or consents to every plan.
The ethical lesson is not that twins owe identical duties. De Bres explicitly rejects the conclusion that twins share all responsibilities and relationships. Instead, a shared project can generate a joint obligation in addition to personal obligations. If both have undertaken a commitment, each may have reason to support it; if only one has made a promise, the other is not automatically bound.
The framework also protects against a subtler form of erasure. Treating a very close pair as “basically one person” can make one sibling’s consent, privacy or disagreement disappear. De Bres’s account insists that acknowledging relational identity should make room for more than one full person, not fewer.
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Common misunderstandings to avoid
- “Shared personhood means one mind.” No. The claim concerns overlapping cognitive practices and commitments, not a single stream of consciousness.
- “Twins are naturally telepathic.” No. Extended-mind and transactive-memory ideas explain coordination through cues, trust and information exchange; they provide no evidence of mind-reading.
- “Every twin pair shares identity in the same way.” No. De Bres writes from a particular close relationship, and the degree of sharing differs among people and across situations.
- “A shared body proves a shared person.” No. Conjoined twins’ self-understandings show that one body can contain distinct persons; bodily arrangement alone does not settle the issue.
- “A different genetic profile creates another person.” No. Chimerism demonstrates biological complexity, not an automatic multiplication of persons.
- “Relational identity cancels individuality.” No. The argument is that connection can be part of individuality without replacing private perspectives, choices and duties.
How to assess the autobiographical evidence
Personal testimony is especially valuable for a philosophical question about lived experience. De Bres can describe what it feels like to rely on Julia’s memories or to act as a pair in a way an abstract definition cannot. At the same time, an autobiography cannot establish how common these experiences are, whether they occur to the same degree in other twins or whether twins differ from other long-term collaborators.
Read the essay, therefore, on two levels. Its examples are evidence that shared cognition, agency and identity are intelligible possibilities. Its broader conclusion—that personhood may be relational and variable—is an argument that readers can evaluate, not a statistical generalisation about a population.
Questions the essay leaves each reader
The twin case is vivid because most readers have experienced smaller versions of its structure. A colleague may remember a project’s history better than you do; a partner may be part of how you make a difficult decision; a community may become central to who you are. The philosophical questions are:
- Which memories do you retrieve through another person’s knowledge?
- When have you formed a commitment that is genuinely a “we” commitment rather than two parallel intentions?
- Which relationships belong to your self-description without defining all of you?
- Where should shared responsibility stop, and where should individual consent remain decisive?
These questions do not prove that every close relationship creates shared personhood. They show why the twin example matters beyond twins: it tests whether our concept of individuality can acknowledge dependence without treating dependence as a defect.
Further reading
De Bres develops the subject at book length in How to Be Multiple: The Philosophy of Twins (2023). The Aeon essay offers a concise route into its three-part framework—shared cognition, plural agency and shared identity—while keeping the emphasis on philosophical interpretation rather than unverifiable claims about all twins.
The takeaway
Being a twin does not make someone less individual. It can make the limits of an overly narrow idea of individuality easier to see. A person may think with another, commit as part of a “we” and include a relationship in her identity while remaining a distinct subject with her own boundaries. De Bres’s argument asks us to treat those layers as compatible: individuality can be real without being solitary.
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