Edwin Hartman's 1977 chapter "Continuity and Personal Identity" (in Substance, Body and Soul: Aristotelian Investigations) defends an Aristotelian, body-based criterion of personal identity against the brain-transplant objection, but concedes that Parfit's fission arguments and Nagel's split-brain cases reveal real limits of any purely bodily criterion: survival can occur without numerical identity, and the number of persons in one body may be indeterminate or a matter of degree. Hartman notes that Aristotle himself possessed an unused resource — a criterion of mental unity as mutual accessibility of conscious contents (De Anima I 5 and III 2) — but never applied it to human persons. The chapter closes with three linked open issues: (i) whether a refined Aristotelian theory incorporating Aristotle's own unity-of-consciousness criterion can give a satisfactory account of personal identity covering both ordinary and extraordinary cases; (ii) how to individuate and count persons at a time in split-brain-type cases, and whether the person as a unitary subject of experience can be maintained; and (iii) whether the moral and prudential significance of death and personal identity must be rethought if psychological connectedness, not identity, is what matters in survival. The later literature (animalism, neo-Lockeanism, the unity-of-consciousness and split-brain literature, and the ethics of death) leaves all three components actively contested, with no consensus resolution.

Background

The persistence question of personal identity asks what it takes for a person existing at one time to be numerically identical with a being existing at another time — what determines which past or future being is you. One long tradition, descending from Locke, answers in psychological terms: a past or future being is you just in case she is psychologically continuous with you now, where psychological continuity is an overlapping chain of psychological connections (memory, intention, character) holding between person-stages. A competing tradition is Aristotelian. In Aristotle's hylomorphism, a living thing is a compound of matter (the body) and form, and the soul is the form of the living body — roughly its functional organization as a living, sensing, rational being — not a separable immaterial thing. On this view a person is identical with the living body, and personal identity is a special case of the identity of a substance through time. This view faces classical difficulties. Ackrill argued that the form–matter distinction collapses for living beings, since neither the living body nor its soul can exist without the other. The brain-transplant (brain-switch) thought experiments of the 1960s literature suggest that a person goes with a transplanted brain rather than staying with the original body, apparently falsifying any bodily criterion. Two further challenges were pressed in the early 1970s. Parfit argued that psychological connectedness can hold one-to-many: if a brain is divided and each hemisphere transplanted into a different body (fission), each resulting person is psychologically continuous with the original, yet the original cannot be numerically identical with both; so what matters for survival is psychological connectedness itself, not numerical identity. Nagel's discussion of commissurotomy ("split-brain") patients — people whose corpus callosum, the neural band connecting the cerebral hemispheres, is severed — argued that such a body may host two partially independent centers of consciousness, so that even the synchronic question of how many persons are in one body may lack a determinate answer. Hartman's chapter defends the Aristotelian criterion: he answers Ackrill by reading form and matter as accidentally identical under different descriptions, and answers the brain-switch objection by appeal to Aristotle's Metaphysics Z 10 claim that a "dominant" part (heart or brain) carries the formula of the substance, so sameness of the dominant organ can serve as the criterion of bodily and hence personal identity. But he concedes that Parfit's and Nagel's cases show bodily continuity alone does not capture everything that matters, and he observes that Aristotle's own texts — De Anima I 5 (divided insects, each part with its own sensations and desires) and III 2 (perceiving differences requires one faculty with access to both contents) — contain a criterion of mental unity as mutual accessibility of contents that Aristotle never applied to human persons. The modern descendants of the Aristotelian view are animalism (the view that we are human animals, with brute-physical persistence conditions) and explicitly hylomorphic varieties of it; their central unresolved difficulties — transplant and teletransportation ("transfer") objections, the remnant-person problem (what is left behind, and what it is, when a person's cerebrum is transplanted into another body), and the too-many-thinkers problem (that wherever we thought there was one thinker, there appear to be two, a person and an animal) — are precisely the extraordinary cases Hartman flagged. The psychology-side literature on split-brain patients and the unity of consciousness, and the ethics literature on death's badness and self-concern given Parfit's reductionism, track his other two residual questions.

Problem Statement

Determine whether a refined Aristotelian theory of personal identity can be completed — that is, whether the framework's core commitments (a person identical with a living body, the soul as its form) can be refined into a satisfactory account of personal identity covering both ordinary and extraordinary cases — or whether no such refinement of the Aristotelian framework can succeed. The chapter's closing discussion raises three linked open issues:

(1) The core metaphysical issue: whether a hylomorphic, substance-based account of personal identity — a person identical with a living body, soul as its form — can be refined to incorporate the criterion of mental unity Hartman identifies as an unused Aristotelian resource, unity of a mind as mutual accessibility of conscious contents along the lines Aristotle applies in De Anima I 5 and III 2, and to yield principled, non-ad-hoc verdicts not only for ordinary cases of persistence but also for the extraordinary cases: brain transplantation, fission (division with each successor psychologically continuous with the original), teletransportation, and split-brain (commissurotomy) patients.

If the framework can be refined, a solution to (1) must state the refinement's persistence conditions, derive a verdict for each of the listed cases — ordinary persistence and the four extraordinary cases — and show those verdicts are not ad hoc by deriving them from the framework's stated commitments; if no refinement succeeds, it must instead state the impossibility argument and show why no such conditions and verdicts can be derived.

(2) The synchronic individuation issue: within such an account or its rivals, how many persons exist in a single body in split-brain-type cases, and whether personhood at a time is determinate or a matter of degree — in particular, whether the notion of a person as a unitary subject of experience can be maintained.

(3) The practical issue: given the outcome of (1) and (2), what the prudential and moral significance of personal identity and death is — whether the ordinary fear of death and special self-concern for one's own future are rational if survival without numerical identity is possible.

These three issues are linked: (1) is the primary question, and (2) and (3) are to be answered from its outcome — from the refined account if it succeeds, or from its rivals and the negative outcome if none does.

References

  1. Edwin Hartman, 'Chapter Three. Continuity and Personal Identity', in Substance, Body and Soul: Aristotelian Investigations, Princeton University Press (1977; Princeton Legacy Library ebook 2015), pp. 88–130. DOI: 10.1515/9781400869411-005 (JSTOR chapter DOI: 10.2307/j.ctt13x156j.7). https://doi.org/10.1515/9781400869411-005
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