1. See, Summa Theologiae [hereafter ST], Ia 75.4, and Quaestiones de Anima [hereafter QDA], 1. Aquinas also claims that the human being is identical to the human person (ST, Ia 29.1 and 4), and he denies that I am identical to my soul (Ad Corinthios, 15, Commentary on Job, Lectio 2).

2. See, De Ente et Essentia [hereafter DEE], 2 and ST, Ia.75.4, where Aquinas argues that matter needs to appear in the very essence of a human being. That is, anything that satisfies the definition of ‘human being’ must possess a body; there can be no disembodied human beings.

3. See Lynne Rudder Baker's characterization of substance dualism: ‘According to mind/body dualism, if Jane is a human person living in Canada, she has a body, but Jane's existence does not depend on her having the body that she has or on her having any body at all: If mind/body dualism is correct, even though she is now embodied, Jane could exist as a purely immaterial being’; Baker, Lynne Rudder ‘Need a Christian be a mind/body dualist?’, Faith and Philosophy, 12 (1995), 489–504CrossRefGoogle Scholar.

4. In fact, there's some debate over whether Aquinas's position is fairly characterized as dualism at all. Stump, Eleonore ‘Non-Cartesian substance dualism and materialism without reductionism’, Faith and Philosophy, 12 (1995), 505–531CrossRefGoogle Scholar, suggests the label ‘subsistence dualism’, although she herself calls Aquinas a non-reductionist materialist, and argues that the dichotomy which contrasts materialism with dualism is harmful rather than philosophically useful.

5. Aquinas holds that for something properly to be called an individual substance, it needs to meet two conditions: (1) it must be capable of independent existence; and (2) it must be complete in species and genus. The body fails both of these conditions; the soul meets (1), and so in this limited sense it can be called a substance, but it fails (2), and so Aquinas claims that the soul isn't a complete substance. (See QDA, 1.co, and ST, Ia 75.2.ad1.)

6. ‘Non enim corpus et anima sunt duae substantiae actu existentes, sed ex eis duobus fit una substantia actu existens’ (1461). All paragraph numbers correspond to the Marietti edition of the Summa Contra Gentiles (Turin: Marietti Editori Ltd, 1961). All translations are mine.

7. This question itself presupposes that Aquinas has successful answers to two prior questions that lie beyond the scope of this paper: (1) Can the human soul continue to exist at death; and (2) What could ground the individuation of separated souls? For discussions of the first question, see Norman Kretzmann The Metaphysics of Creation: Aquinas's Natural Theology in Summa Contra Gentiles II (Oxford: Clarendon Press, 1999), and Robert Pasnau Thomas Aquinas on Human Nature: A Philosophical Study of Summa Theologiae Ia 75–89 (Cambridge: Cambridge University Press, 2002). For a detailed discussion of the second question, see Bazán, Bernardo ‘La corporalité selon Saint Thomas’, Revue Philosophique de Louvain, 81 (1983), 369–409CrossRefGoogle Scholar.

8. The identity claim here about body and soul differs importantly from the identity claim ‘David is identical to his body’, where we would typically agree that David can, nevertheless, persist through changes in body parts (such as a foot amputation or a heart transplant). The latter case is significantly complicated by the difficulty specifying the diachronic identity conditions for material objects (illustrated by examples such as the ship of Theseus), whereas the former case involves a composite not of physical but of metaphysical parts whose continued persistence is necessary for the persistence of the object in question. To see this, compare the claim ‘David is a composite of his body parts’ with the claim ‘David is a composite of form and matter’. We can imagine David's persisting through the loss and/or replacement of individual body parts, whereas it's impossible on a hylomorphic account to imagine David's persisting through a loss either in form or in matter. (For an argument that questions this understanding of hylomorphic identity, however, see Eleonore Stump's discussion of souls, bodies, and the constitution relation in ch. 1 of Aquinas (London: Routledge, 2003), 35–60.)

9. See, for example, Baker ‘Need a Christian be a mind/body dualist?’; Peter van Inwagen (ed.) The Possibility of Resurrection and other Essays in Christian Apologetics (Boulder CO: Westview Press, 1978); and Zimmerman, Dean ‘The compatibility of materialism and survival: the “falling elevator” model’, Faith and Philosophy, 16 (1999), 194–212CrossRefGoogle Scholar.

10. Hughes, Christopher ‘Aquinas on continuity and identity’, Medieval Philosophy and Theology, 6 (1997), 93–108CrossRefGoogle Scholar.

11. For a closely parallel passage, see the Scriptum, IV.43.1.1. Lectiones II–VII of Aquinas's commentary on I Corinthians provide Aquinas's most detailed examination of the doctrine of Christ's resurrection and its consequences for human beings, but they contain little of philosophical interest.

12. Marilyn McCord Adams discusses these arguments in her survey of Aquinas's position on the bodily resurrection; Adams, Marilyn McCord ‘The resurrection of the body according to three medieval Aristotelians: Thomas Aquinas, John Duns Scotus, and William Ockham’, Philosophical Topics, 20 (1992), 2–8CrossRefGoogle Scholar.

13. ‘Ostensum est enim in Secundo animas hominum immortales esse. Remanent igitur post corpora a corporibus absolutae. Manifestum est etiam ex his quae in Secundo dicta sunt, quod anima corpori naturaliter unitur: est enim secundum suam essentiam corporis forma. Est igitur contra naturam animae absque corpore esse. Nihil autem quod est contra naturam, potest esse perpetuum. Non igitur perpetuo erit anima absque corpore. Cum igitur perpetuo maneat, oportet eam corpori iterato coniungi: quod est resurgere. Immortalitas igitur animarum exigere videtur resurrectionem corporum futuram’ (4135).

14. The argument also relies on the rather dubious claim, which Aquinas attributes to Aristotle in his commentary on De Caelo et Mundo (2, 269 b7–10), that nothing contrary to nature can exist perpetually. Fortunately, the soundness of Aquinas's argument isn't relevant to our purposes – what's of interest is what this passage says about the nature of the human soul.

15. ‘Anima autem a corpore separata est aliquo modo imperfecta, sicut omnis pars extra suum totum existens: anima enim naturaliter est pars humanae naturae’ (4136).

16. ‘Anima Abrahae non est, proprie loquendo, ipse Abraham, sed est part ejus; et sic de aliis.’

17. ‘Ceteris paribus perfectior est status animae in corpore quam extra corpus, quia est pars totius compositi’. He makes this point in response to the objection that human souls should remain disembodied because in that state they resemble God and the angels more closely.

18. ‘In nullo enim naturalium rerum invenitur id quod corruptum est idem numero redire in esse: sicut nec ab aliqua privatione ad habitum videtur posse rediri. Et ideo, quia quae corrumpuntur eadem numero iterari non possunt, natura intendit ut id quod corrumpitur idem specie per generationem conservetur. Cum igitur homines per mortem corrumpantur, ipsumque corpus hominis usque ad prima elementa resolvatur: non videtur quod idem numero homo possit reparari ad vitam’ (4139).

19. The objector gets Aristotle's point slightly wrong. What Aristotle actually says in the Physics is more complicated; he claims that if it were true that the two instances of health were not numerically identical, then one would need to be committed to the principle of non-repeatability. And then he claims that ‘these difficulties lies outside our present inquiry’.

20. For more support of this sort of claim in Aristotle, see Gen. et Cor., ii.9, which Aquinas takes to say that the only kind of identity you get after a corruptible substance is destroyed is identity of species, not numerical identity. (Aquinas cites this passage in his Commentary on Job, 19 L.II and his Commentary on I Corinthians, 15 L.IX.)

21. Hughes ‘Aquinas on continuity and identity’.

22. SC, 43.1, q.4.co, opinion 2.

23. Aquinas's Sentences commentary is dated 1253–1256, QQ to 1256–1259, and SCG to 1259–6125. (Dates taken from Norman Kretzmann and Eleonore Stump ‘Aquinas, Thomas’, in Edward Craig (ed.) Routledge Encyclopedia of Philosophy (London: Routledge, 1998).)

24. ‘Philosophus dicit in lib. de anima, quod non est eadem statua numero quae destruitur, et de eodem aere reficitur. Pari ergo ratione corpus quod modo corrumpitur, non erit idem numero cum eo quod resurget’; QQ (Turin: Marietti Editori Ltd, 1956).

25. There's an interesting ambiguity to the example as it's set out in this passage: it's not clear whether Aquinas is thinking of a case in which a statue of Hypatia is melted down and then refashioned as a statue of Xanthippe, or whether he's thinking of Hypatia's statue being melted down and then refashioned as Hypatia again. I take it, though, that Aquinas's answer is going to be the same no matter which case he's thinking of. Even in the case where the statue is refashioned in exactly the same shape, I think Aquinas will claim that it has a different form in each instance, since statue forms are non-repeatable accidents. The case of the forms of the Hypatia statues will be parallel to the case of my suntan last year and my suntan this year – i.e. they're two numerically distinct instances of the same property, ‘being shaped like Hypatia’, or ‘being tan’.

26. ‘[O]mnia artificialia ponuntur dupliciter in genere vel in specie; quia vel per materiam suam, vel per formam suam. Naturalia autem ponuntur in genere vel specie tantum per formam suam. Formae autem artificiales, quia sunt accidentia, idea oportet quod collocentur in genere vel specie per materiam; naturales vero non, quia sunt substantiales.’

27. One might suppose that, were every atom in the refashioned statue B situated precisely where each atom was situated in the original statue A, B and A would count as the same statue. Aquinas would, however, likely point out that this is still an appeal to features of the matter of the statue. His position on artefactual identity relies on sameness of form: the artefactual form of B is numerically distinct from A (in the same way that each miniature replica of Michelangelo's David possesses a distinct artefactual form), and so B and A would count as different statues, despite similarities in matter.

28. There are, of course, cases involving living organisms which appear somewhat vague: suppose that a hamster dies, but that a dedicated veterinarian manages to bring it back to life a moment later. In that case (and similar cases), I believe Aquinas would claim that it is the same hamster (or human being, koala bear, etc.). In cases that involve a greater time-span between the end of biological life processes and reanimation, however, it is more difficult to speculate on Aquinas's behalf. In general, though, it seems to me that the question here involves epistemological difficulties specifying the precise moment at which the substantial form/soul separates from matter, rather than metaphysical difficulties with Aquinas's account of human nature.

29. See ST, Ia.119 and a slightly later passage SCG, IV.81. In both places, Aquinas claims that the matter that composes the human body can change over time without compromising the identity of the human being, so long as the substantial form remains the same.

30. ‘Secundum hoc igitur ad primum dicendum quod virtus naturae deficiens est a virtute divina, sicut virtus instrumenti a virtute principalis agentis. Quamvis igitur operatione naturae hoc fieri non possit, ut corpus corruptum reparetur ad vitam, tamen virtute divina id fieri potest. Nam quod natura hoc facere non possit, ideo est quia natura semper per formam aliquam operatur. Quod autem habet formam, iam est. Cum vero corruptum est, formam amisit, quae poterat esse actionis principium. Unde operatione naturae, quod corruptum est idem numero reparari non potest. Sed divina virtus, quae res produxit in esse, sic per naturam operatur quod absque ea effectum naturae producere potest, ut superius est ostensum. Unde, cum virtus divina maneat eadem etiam rebus corruptis, potest corrupta in integrum reparare’ (4150).

31. Peter van Inwagen ‘The possibility of resurrection’, in idem The Possibility of Resurrection and other Essays in Christian Apologetics, 45–51.

32. Baker ‘Need a Christian be a mind/body dualist?’, 499.

33. Baker's position relies on an interesting version of non-reductionist materialism according to which the human body constitutes the human being without being identical to that human being. See Baker, Lynne Rudder ‘Why constitution is not identity’, The Journal of Philosophy, 94 (1997), 599–621CrossRefGoogle Scholar.

34. I cannot, of course, hope fully to spell out such an account here; the position I lay out here is meant to indicate in outline what such an account would look like.

35. As Montague Brown asks, ‘Granted that there is to be a resurrection of the body with the rational soul providing the transition from this life to the other, would not the break in continuity between the soul's information of the body in this life and its information of the resurrected body rule out the possibility of the person being one and the same in each case?’; Brown, Montague ‘Aquinas on the resurrection of the body’, The Thomist, 56 (1992), 165–207CrossRefGoogle Scholar, 193.

36. Edwards, Sandra ‘Saint Thomas Aquinas on “the same man”’, Southwestern Journal of Philosophy, 10 (1979), 94–95CrossRefGoogle Scholar.

37. See Sydney Shoemaker ‘Identity, properties, and causality’, in idem (ed.) Identity, Cause and Mind (Cambridge: Cambridge University Press, 1984), 234–260; Dean Zimmerman ‘Immanent causation’, in J. E. Tomberlin (ed.) Philosophical Perspectives XI: Mind, Causation, and World (Oxford: Blackwell, 1997), 433–471; Hud Hudson A Materialist Metaphysics of the Human Person (Ithaca NY: Cornell University Press, 2001), especially chs 4 and 7.

38. Zimmerman ‘The compatibility of materialism and survival’.

39. This is, of course, what drives materialists such as Hudson, Van Inwagen, and Zimmerman to claim that a person's life does not end at death, contrary to popular opinion. Rather, God preserves David's life in some way or another by preserving whatever material component of the person is necessary for David's continued identity.

40. The Latin word, esse, is notoriously difficult to render in English in a way that preserves its original meaning. The infinitive form of the verb ‘to be’, esse is used by many medieval scholars (including Aquinas) to indicate the ‘act of existing’ an actual being possesses, where this differs from that thing's essence. Someone could meaningfully describe the essence of a human being (or a hamster), even if no such animal existed at that moment in time. A thing's actuated essence – its existence – is its ‘esse’.

41. ‘Manifestum est enim quod materiae et formae unum est esse: non enim materia habet esse in actu nisi per formam … . Anima vero rationalis, manifestum est quod excedit materiam in operari: habet enim aliquam operationem absque participatione organi corporalis, scilicet intelligere. Unde et esse suum non est solum in concretione ad materiam. Esse igitur eius, quod erat compositi, manet in ipsa corpore dissoluto: et reparato copore in resurrectione, in idem esse reducitur quod remansit in anima’ (4156).

42. I can't hope to defend here Aquinas's claim that the human soul can exist in separation from matter. I think, however, that Eleonore Stump is right in claiming that (1) Aquinas is a sort of non-reductionist materialist, and that (2) non-reductive materialism might create the logical space necessary for a subsistent soul; Stump ‘Non-Cartesian substance dualism and materialism without reductionism’. See also Richard Boyd ‘Materialism without reductionism: what physicalism does not entail’, in N. Block (ed.) Readings in Philosophy of Psychology, vol. 1 (Cambridge MA: Harvard University Press, 1980).

43. This, I take it, is the main force of the arguments Aquinas makes in SCG, IV.81 on behalf of the continuity of the essential principles of the human being. For a defence of this claim in more contemporary terms, see Eleonore Stump's discussion of Aquinas's account of identity post-death and the continuity of a configured configurer in Aquinas, chs 1 and 4; see also Robert Pasnau's discussions of this topic in Thomas Aquinas on Human Nature.

44. Again, it's crucial for Aquinas's explanation of post-resurrection identity that David's esse continues after his death, preserved by his soul. This is what allows Aquinas to claim that David's resurrected self constitutes a different stage of the same life, rather than constituting the beginning of a new person who's qualitatively identical to David.

45. See Van Inwagen ‘The possibility of resurrection’, and Zimmerman ‘The compatibility of materialism and survival’.

46. Earlier drafts of this paper were read at the Cornell Colloquium in Mediaeval Philosophy, St Louis University, and the University of Akron, and I owe those audiences my thanks for their helpful comments. I am especially grateful to the Philosophy Department at Calvin College for their feedback, to Scott MacDonald for his comments on various stages of this paper, and to Justin Kincaid for working through the final formatting issues.