Academic journal article The Review of Metaphysics

St. Thomas on the Incorruptibility of the Human Soul: A Reassessment of His Argument from Natural Desire

Academic journal article The Review of Metaphysics

St. Thomas on the Incorruptibility of the Human Soul: A Reassessment of His Argument from Natural Desire

Article excerpt


In question 75, article 6 of the first part of his Summa Theologica, St. Thomas asks "whether the human soul is incorruptible." After considering various arguments pro and con, he answers in the affirmative as follows:

   [E]ach thing naturally desires its own manner of being. Now, in
   things that have knowledge the desire follows the knowledge. A
   sense, however, does not know being except as here-and-now. By
   contrast, the intellect apprehends being in an absolute sense and
   in respect of all time. It follows that all things that have an
   intellect naturally desire to exist always. However, a natural
   desire cannot be in vain; consequently an intellectual substance is
   incorruptible. (1)

Historically, this argument has been extremely negatively evaluated, most famously perhaps by John Duns Scotus who said:

   Every argument based on natural desires seems to be inconclusive,
   for to construct an effective argument it would be necessary to
   show either that nature possesses a natural potency for eternal
   life, or that the knowledge which immediately gives rise to the
   desire ... is not erroneous but in accord with right reason. The
   first alternative is the same as the conclusion to be established;
   the second is more difficult to prove and is even less evident than
   the conclusion. (2)

I believe that Scotus's critique may not be as telling as traditionally has been thought. Specifically, I believe that the ontological grounding of the intellective soul's capacity to apprehend being--which distinguishes it from nonintellective souls--plays a much more important role in Aquinas's argument than Scotus appears to acknowledge, and that when this ontological grounding is granted and analyzed in terms of the Aristotelian metaphysics of substantial forms, St. Thomas's argument is different from and much stronger than Scotus thinks. I also believe that if the notion of natural desire is understood in ontological terms--and I shall give reasons for saying that St. Thomas understood it in that fashion--Scotus's dismissal of its role may have to be reexamined. Finally, I believe that if St. Thomas's argument is unpacked as an enthymeme that assumes the reader's familiarity with Aristotle's discussion of the soul in the De anima, what emerges overall is an argument that is quite different from how it has traditionally been understood.

In what follows, I shall reconstruct St. Thomas's argument using contemporary conceptual tools, and I shall make three assumptions: first, that the word "follows" (sequitur) used by St. Thomas to relate incorruptibility to natural desire should be understood in a logical, rather than a causal sense; second, that the notion of a natural desire should be understood in an ontological rather than a subjective psychological sense; and third, that the claim about the relationship between natural desire and incorruptibility should be seen as a claim about what is entailed by the ontology of human souls as substantial forms, not as a claim about the validity of natural desires in psychological terms. These assumptions will be defended either by reference to St. Thomas's own words or by relating them to conceptual features inherent in the theories of Aristotle to which St. Thomas subscribed.


To begin with the word "follows." The word that St. Thomas uses, sequitur, has several meanings in medieval Latin. One is to associate two states of affairs in a sequential temporal relationship, where one succeeds the other in time; another is to relate states of affairs in causal terms, where one member in the sequence is causally dependent on the other; and a third is to associate the relata in logical terms, where what "follows" is logically implied by and derivable from the other.

The relationship when the term is understood in the first two senses is fundamentally different from the relationship as understood in the third sense. …

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