Summa Theologiae 1, qq. 75-89 & 93

The Essence and Powers of the Human Soul and
the Human Soul as the Image of God

Question 75:  The Essence of the Human Soul
Question 83:  Free Choice
Question 76:  The Relation of the Soul with the Body
Question 84:  How the Conjoined Soul Understands Corporeal Things That Are Below Itself
Question 77:  The Powers of the Soul in General
Question 85:  The Mode and Order of Intellective Understanding
Question 78:   The Specific Powers of the Soul
Question 86:  What Our Intellect Has Cognition of in Material Things
Question 79:  The Intellective Powers Question 87:  How Our Intellect Has Cognition of Itself and of What Exists Within It
Question 80:  The Appetitive Powers in General
Question 88:  How the Human Soul Understands Things That Are Above It
Question 81:  The Sentient Appetite Question 89:  A Separated Soul's Cognition
Question 82:  The Will Question 93:  The End or Terminus of the Production of Man

Question 75:  The Essence of the Human Soul
  • General Comments:  The two opening questions of the so-called "Treatise on Human Nature," q. 75 and q. 76, are among the most difficult in the Summa Theologiae, the difficulty being compounded by the fact that one needs to understand a significant amount of Aristotelian background in order not to be misled by various claims and arguments made by St. Thomas.  For this reason,extreme caution is called for.  But the rewards of careful reading are great.  For we begin to see here St. Thomas's via media between dualism (in both its Platonic and Cartesian versions) and materialism, i.e., the denial of the immateriality of the human soul.

  • 75, 1:  The important thing to see here, right away, is that an argument for the claim that a soul is not a body is not an argument for the immateriality or incorporeality of souls in the usual sense.  The reason is that on an St. Thomas's Aristotelian ontology there are two ways of being incorporeal.  One is to be a (substantial) form that constitutes a matter with appropriate potentialities as a body, i.e., bodily substance, of a given natural kind.  The other is to be a subsistent immaterial entity that (a) can come into being only through creation ex nihilo and not through generation and that (b) has no intrinsic principles of corruption.  In article 1 St. Thomas is arguing only that a soul -- any soul -- is incorporeal in sense (a); in this article, he has nothing to say about (b).  The form of the argument he uses here could just as easily be amended to show that, say, the shape of a statue is not a body, since not every body is a statue of that shape.  However, it is of course true that St. Thomas is here focusing on living bodies, and so, since a soul is the form of a living bodily substance, his main aim is just to spell out a few truths about souls in general and at the same time to put into question a couple of dominant, though mistaken, ideas about souls.

    In arguing for the claim that the soul is the form or act or actuality of a living body, St. Thomas first notes that two of the principal activities associated with living things are movement and cognition.  Now movement here should be construed broadly as change in general and not just local movement, i.e., movement in space.  The soul is often called "the mover of the body," since it is ultimately responsible as a first principle for various 'vital operations' that characterize living bodily substances, e.g., nutrition, growth, reproduction, self-initiated local motion, along with cognition and affection of various sorts.  But on St. Thomas's view it is important to understand this "moving" relation correctly.  He will not accomplish this completely in the present article, but he will make a beginning.  The same holds for what he has to say here specifically about cognition.  In both cases, his main targets are errors committed by some of the pre-Socratic philosophers.  Specifically, they held that (a) only bodies can be movers of bodies and so a soul, because it moves a body as a principle of vital operations, must be a body, and (b) cognition of bodies takes place only through a union of likeness and similitude, and so an animal or human soul, because it is a principle of the cognition of bodies, must itself be a body (or an array of bodies such as water, air, earth and fire) in order to have the required likeness or similitude to the objects of cognition.

    The main argument for the claim that the soul is not a body, i.e., a bodily substance, is that if we take for granted (a) the definition of a soul as a first principle of life and (b) the fact that not every bodily substance is alive, then a soul is that in virtue of which a bodily substance is alive.  It follows that a soul is the act or form of a living body and not itself a body.

    As for movement, the soul as a first principle of a living thing is the first principle of all the vital movements in it.  So it moves the bodily substance of which it is the form.  But it obviously does not have quantitative contact with the body of which it is the form.  So if we want to insist that a mover must have contact with what it effects movement in, let's just say that the soul has contact of power with the body.  (We would have to say the same thing in cases where immaterial subsistents (God or angels) effected movement in matter.  Later we will get more details about the appetitive powers of the soul and their relationship to change.)

    As for cognition, the soul does not need to be actually composed of fire, air, earth, and water in order to have cognition of bodily things.  It does need to have the capacity or potentiality to "become" in some sense the things it has cognition of.  We will say more of this sort of union between known and knower later in the treatise on human nature.

  • 75,2:  What was said above does not entail that any soul is itself a subsistent being with operations or activities that are in themselves "not shared with" the body that the soul constitutes as a living thing.  That would require a special argument, and St. Thomas thinks that an argument of this sort is available only for the human soul with respect to its intellective operations, viz., intellective understanding of the natures of things (and whatever other forms of abstract thought come along with this) and intellective appetite or willing.

    Notice right away that this separates St. Thomas from both Plato and Descartes, both of whom attributed sensings and feelings to an incorporeal and subsistent being.  He is fully aware of this in the case of Plato, as becomes clear in a. 3: "Now Plato did distinguish intellective understanding from sensation, but he attributed both of them to an incorporeal principle, arguing that just as intellective understanding belongs to the soul in its own right, so too does sensing. And from this it followed that even the souls of brute animals are subsistent."

    In any case, St. Thomas's brief argument is that if the human soul were not subsistent and hence not incorporeal or immaterial in a stronger sense than that established in a. 2, then it would not be able to have intellective understanding of the natures of all bodies.  The idea is that the very makeup of the soul or of any corporeal instrument would impede an intellective cognition of the natures of material substances, where an intellective cognition is characterized by its abstraction from the "material conditions" of the here and now.  

    Before we look at the argument more closely, let's remind ourselves -- if we need reminding -- about the vast gulf that separates human cognition from the sort of cognition had by brute animals:

    • First of all, there's a difference in generality.  That is, I can talk about, say, black holes or aardvarks or red oak trees in general or triangles or 43151 students in general, without having any particular in mind.  

    • Again, I am able to perceive this thing that I sense not just as a collection of a certain set of colors and shapes, say, but as an aardvark; in other words, intellective understanding surpasses in insight anything that a non-rational animal can have by way of cognition of material substances.  (Empiricists like Hume in effect deny this, but why think they're right about this?  We perceive plants and animals and computers, etc., in such a way as to be able to taxonimize them for further study.  And notice that Kant would never have ended up where he did if he had not accepted Hume's impoverished views about the nature of human sensation in the first place.)

    • Not only can we grasp the natures of things, we can affirm or deny claims about them and their characteristics, and reason discursively (whether deductively or inductively or abductively) about them.  That's how we get through ordinary life and how we do science to boot.

    • We can do mathematics!  That's pretty amazing all on its own.

    • We can plan ahead.  Who else but human beings could get themselves worried to a frazzle about how, say, their kids are going to turn out, or about global warming, etc.

    • We do science, give lectures about how we're not much different from apes, build universities, engage in commerce, make stuff in factories, commit mass murder for political causes, play baseball, make statues and portraits of important human beings of the past, etc. -- none of which, as far as I know, apes do.
Now let's start thinking about material things or processes that might putatively serve as the medium of thought.  They all seem to be such that they have to be endowed with meaning by something outside themselves.  This is certainly the case with spoken and written language, as well as with mathematical notation.  But doesn't the same thing hold for brain states and processes as well? (It doesn't seem that the same holds for sensory cognition -- whether exterior (seeing, hearing, tasting, etc.) or interior (remembering, imagining) as such.)  Take an example that Ross adapts from Wittgenstein and Kripke.  I add 2 + 8 and come up with 10.  My thought is the actualization of a function that I myself can distinguish from closely related functions, even some that will never in the history of the world give different results.  Take, for instance, a function that for any two natural numbers, yields exactly the same results as addition for the first 250,000,000 years of the universe's existence, but yields x + y + 8 after that.  Call this function 'quaddition'.  Every mere material representation of any actual instance of genuine adding is indistinguishable from a corresponding material representation of an instance of quadding.  Yet I can know that when I now take 8 and 2 as arguments and get 10 as an answer that I am adding and not quadding.  A material process (say, in an adding machine or in the calculator program on my computer) might simulate addition, but it is also at the same time simulating quaddition.  Not me, though.  I'm adding and not quadding.  Therefore, whatever I am doing is not a material process, even if my doing it depends in part on material processes; therefore, it is immaterial.  Something similar holds for my grasp of a nature, whether it be a material nature such as aardvarkiness or some quantitative nature (say, triangularity) abstracted from all matter except for its purely quantitative properties.  We will ponder this more when we look at intellective understanding in more detail in questions 84, 85, and 86.

In the meantime, let me try a defensive tactic here.  People enthusiastic about the ability of neuroscience to undermine the claim to immateriality (see Tom Wolfe's essay "Sorry, but Your Soul Just Died") need to tell us in general what their "success" would like like.  Suppose they identified certain species or patterns of neuro-processes that correlated with, say, thinking scientifically about aardvarks or triangles.  (Perhaps identifying just correlations with speaking about aardvarks or triangles wouldn't do it, for reasons like those given above.)  Would it then be reasonable to identify those processes with thinking about aardvarks (triangles)?  Only, it seems, if they wore their meaning on their sleeves.  But they don't, or at least it's hard to see how they would.  (Some of John Searle's reflections seem relevant here.)

In any case, we can keep thinking about these issues as we go through St. Thomas's treatment of intellective understanding and willing.

Note the replies to the objections:  The soul is a 'this-something' because it is subsistent, but it is not a 'this-something' in the sense of being a subsistent thing that is complete in a species, since it is only a 'part' (albeit the most important part) of a human being, viz., his form.  Again, strictly speaking, it is better to say that a man thinks by means of his soul rather than to say that the soul thinks.  (Later we will worry about the status of the separated soul.)  Finally, we have to distinguish the sort of dependence that the soul has on the body in its intellective operations, viz., it depends on the body for the main objects of its thought, from the sort of dependence it would have if its operations were, like sensings and feelings, the acts of a corporeal organ.  It is the latter that St. Thomas denies.

So these first two articles have been aimed at showing that the human soul is (a) the form of a human body, (b) incorporeal, and (c) subsistent with its own proper operations.

  • 75, 3: