Everyone seems to want Aristotle on their side. Thomists interpret him as a Thomist. Virtue ethicists interpret him as a virtue ethicist. Functionalists interpret him as a functionalist. Materialists interpret him as a proto-scientific naturalist who just happened to have some slightly wonky metaphysical views. In this essay, I argue that, when it comes to philosophy of mind, the Thomists are right: Aristotle held what can be described as a broadly "Thomistic" philosophy of mind; or, to put things differently, Thomas Aquinas was a more objective interpreter of Aristotle's philosophy of mind than is sometimes thought.
1. A Thomistic interpretation of Aristotle's philosophy of mind: four theses
What I'm describing as a "Thomistic" interpretation of Aristotle's philosophy of mind consists of four basic theses:
- The human soul is united to the body as a form. In more contemporary terminology, we might say that the soul is united to the body as a property.[1]
- The human intellect, i.e. a human being's ability to think, has the human soul as its subject.
- The human intellect is immortal and separable from the body.
- What separates from the body at death is not the intellect alone but, rather, the soul, which carries the intellect away with it.
These four theses don't come close to exhausting Aquinas's interpretation of Aristotle's philosophy of mind. Nonetheless, they are sufficient to separate a Thomistic interpretation of Aristotle from other modern interpretations.[2] The first thesis is fairly uncontroversial,[3] and I won't spend time defending it. Let's now turn to my defense of the other three theses.
2. The second thesis
Aristotle insists that the intellect isn't "mixed with the body" (DA 429a21-25).[4] This implies that the intellect doesn't have the body as its subject: in other words, the body isn't what has the ability to think. So what does have the ability to think? Aristotle suggests an answer when he calls the intellect "that part of the soul by which the soul both knows and understands" (DA 429a10). By this, Aristotle implies that the soul itself has the ability to think. Just as the soul is a property of the body, so the intellect is a property of the soul: the soul is "stacked", so to speak, on top of the body, and the intellect is stacked on top of the soul.
In contrast to the second thesis, some Aristotelian scholars interpret the intellect as an immaterial substance separate from the body. Lloyd Gerson (2004) explicitly endorses such an interpretation.[5] This kind of interpretation gains apparent support from Aristotle's (rather offhand) remark that the intellect is "born in us as a kind of substance" (DA 408b17).
However, such an interpretation contradicts Aristotle's explicit statements. According to Aristotle, the soul is united to the body as a form. So, if the intellect is a substance separate from the body, then the intellect can't be part of the soul. (Indeed, Gerson explicitly says that, on his interpretation, the intellect is not part of the soul.) Yet Aristotle clearly regards the intellect as part of the soul (cf. DA 429a10, Metaph. 1070a23-27).
According to other scholars, when Aristotle says that the intellect isn't mixed with the body, he simply means that the intellect doesn't have its own bodily organ. On this interpretation, the intellect is a property of the whole body, not of any particular organ. Michael Wedin (1993) accepts a version of this interpretation in his "functionalist" interpretation of Aristotelian cognitive abilities. Victor Caston (2006, 337) also takes this view, and summarizes it nicely:
[Aristotle's remarks about the intellect] need mean no more than this: that there is no organ of understanding, that is, no discrete part of the body that is dedicated to its functioning, as there is for each of the other capacities that make up the soul. […] [The intellect] is part of the form of the body, but it is not the form of part of the body.
The trouble with this interpretation is that it makes Aristotle inexplicably redundant.[6] Consider the passage in which Aristotle denies that the intellect is mixed with the body:
Hence, too, it is reasonable that it should not be mixed with the body; for in that case [i.e. if the intellect were mixed with the body] it would come to be of a certain kind, either cold or hot, or it would even have an organ like the faculty of perception; but as things are it has none. (DA 429a24-27)
Here Aristotle makes two apparently distinct claims: (1) the intellect isn't mixed with the body; (2) the intellect doesn't belong to any particular organ. According to the interpretation currently under consideration, these two claims mean exactly the same thing; thus, I conclude that that interpretation is wrong.
Given the failure of these alternative interpretations, I conclude that the best interpretation is the one offered by the second Thomistic thesis: the intellect is a property of the soul itself. In one passage, Aristotle seems to confirm this interpretation: "Those who say, then, that the soul is a place of forms speak well, except that it is not the whole soul but that which can think" (DA 429a27-28). The "forms" in question here are apparently intelligible forms, the forms which one receives when thinking and which constitute thoughts (cf. DA 429a15, 431b29–432a1, 431b1). The implication, then, is that the soul receives intelligible forms. Since the intellect is, roughly, the ability to receive intelligible forms, it apparently follows that the intellect is a property of the soul itself.[7]
3. The third thesis
Aristotle calls the intellect "separable" and "immortal" (cf. DA 413b24-26, 429b5-6, 430a17-18). Thus, one might think that the third thesis is beyond dispute. Yet a number of scholars have objected to it. Here I will focus on only one major objection—that of Victor Caston. Caston (2006, 340-41) argues that, when Aristotle speaks of a "separable", "immortal" intellect, he's referring to the divine intellect, not the human intellect.
Unfortunately for Caston's interpretation, Aristotle explicitly attributes the separable, immortal intellect to the soul (DA 413b24-26). Caston recognizes this, but he proposes that the soul in question is "either (1) one of the higher intelligences, as many of the medieval Arabic and Italian Renaissance commentators hold, or (2) God himself" (Caston 2006, 339). This proposal simply won't do. Aristotle defines the soul as the body's form; therefore, God and the celestial intelligences can't have souls, because they don't have bodies.
Moreover, consider the following passage from the Metaphysics:
Now in some cases the 'this' does not exist apart from the composite substance, e.g. the form of house does not so exist […] For when a man is healthy, then health also exists; and the shape of a bronze sphere exists at the same time as the bronze sphere. But we must examine whether any form also survives afterwards. For in some cases this may be so, e.g. the soul may be of this sort—not all soul but the reason; for doubtless it is impossible that all soul should survive. (1070a13-14, 23-27)
Here Aristotle notes that a form usually can't exist apart from the matter-form composite of which it's a part: a house's form can't exist apart from the house, nor can health exist apart from a healthy person. Aristotle then says that the intellect may be an exception to this rule. In other words, the intellect may be able to exist apart from its matter-form composite. Here Aristotle is clearly talking about the separable, immortal intellect that we've been discussing. But he can't be talking about a divine intellect, because a divine intellect is not, and never was, part of a matter-form composite.
I conclude that the third thesis is true: Aristotle regards the human intellect as immortal and separable from the body.
4. The fourth thesis
4.1. Why the fourth thesis?
My support for the fourth thesis rests not on strong textual evidence but, rather, on its usefulness in tying together the loose ends created by the other theses. If the soul is the body's form, the intellect is a property of the soul, and the intellect is no more than the ability to think, then how can the intellect exist "on its own", apart from the body? After all, every ability is an ability of something: the notion of a separate, free-floating ability is incoherent. The answer to this question seems obvious to me: the disembodied intellect doesn't exist "on its own"; rather, the disembodied intellect exists as a property of the disembodied soul. For this answer to be true, the fourth thesis must be true: the (human) soul itself must be able to exist apart from the body.
Before considering some potential objections to the fourth thesis, I should make clear what the fourth thesis doesn't claim. It doesn't claim that a soul can exist as a soul apart from the body. Such a claim would contradict Aristotle's assertion that "the soul does not exist without a body" (DA 414a20). Instead, the fourth thesis claims that the soul can separate from the body—at which point it ceases to be a soul, just as a severed hand is no longer a hand (cf. Pol. 1253a20-22).
The fourth thesis may gain some textual support from Aristotle's notorious analogy between the soul and a sailor: "It is not clear whether the soul is the actuality of the body in the way that the sailor is of the ship" (DA 413a7-9). This statement comes after Aristotle's claim that the soul is the body's form. Thus, the statement is rather puzzling. A sailor is the "actuality" of his ship only in the sense that he controls his ship's activity; he certainly isn't his ship's form in the way that the soul is the body's form. I can think of only one way to make sense of Aristotle's sailor-soul analogy: just as a sailor can exist apart from his ship, but ceases to be a sailor when he does so, perhaps the soul can exist apart from the body, but ceases to be a soul when it does so. If this is the correct interpretation of the statement, then the statement shows that Aristotle regards a disembodied (ex-)soul as a possibility.
I will now address three major potential objections to the fourth thesis.
4.2. The first objection
The fourth thesis may seem incompatible with the reasoning that led me to endorse it. I endorse it partly because I can't see how the intellect, as nothing more than an ability, could exist "on its own". Now, according to a widespread interpretation, an Aristotelian soul is a set of abilities—namely, the set of abilities associated with life (cf. Witt 1989, 136; Caston 2006, 337). If the soul is just a set of abilities, and abilities can't exist "on their own", then it would seem that (contrary to the fourth thesis) the soul can't exist apart from the body.
In response to this objection, I deny that an Aristotelian soul is a set of abilities. Rather, the soul is a property which, when present, confers various abilities upon the body.[8] It would take me far afield to do all the metaphysical work necessary to argue fully for this. For now, I'll simply note the following: if the second thesis is true, then the soul probably isn't a set of abilities. According to the second thesis, the ability to think belongs to the soul. And it's at least unclear what it would mean for an ability to belong to a set of abilities.
4.3. The second objection
Here's the second objection. If the second Thomistic thesis is correct, then the intellect is "part" of the soul only in the sense of being a property of the soul. Now, the intellect seems to be the only part of the soul whose separability Aristotle recognizes. It seems, then, that the soul itself isn't separable from the body at all; only the intellect is.
In response to this objection, I will simply note that Aristotle is unclear on this point. True, he says that "parts" of the soul besides the intellect aren't separable from the body (cf. DA 413a4-5). But what does "part" mean here? Does it mean a component of the soul, or does it simply mean one of the abilities stemming from the soul? If it means the latter, then the claim that most "parts" of the soul are inseparable from the body doesn't threaten the fourth thesis.[9]
4.4. The third objection
Lastly, one might argue that the fourth thesis is simply absurd. For Aristotle, the soul is united to the body as some kind of property. Properties, one might argue, simply can't separate from their bearers. For example, the whiteness of a white sheet of paper can't separate from the sheet of paper. The sheet of paper can cease to be white (for example, if I burn it), but in that case the whiteness simply ceases to exist; it doesn't separate from the sheet of paper. How, then, could the intellect separate from the body?
My response to this objection is a bit complicated. First of all, the question we should be asking isn't "How could the soul possibly separate from the body?" Rather, the question is "Why shouldn't the soul be able to separate from the body? What specifically Aristotelian principle might prevent that from happening?" The answer seems to lie in Aristotle's rule that multiplicity requires matter (1074a33-37): roughly, if multiple things have the same form, then the only thing that can differentiate them is matter. This rule—call it the matter rule—seems to entail that souls can't exist (at least as distinct individuals) apart from bodily matter. If one is going to argue against the fourth thesis, then one ought to take one's stand on the basis of the matter rule.
Now let's get clear on what the matter rule entails. The matter rule rules out the existence of matterless disembodied souls (or ex-souls, to be precise, since a disembodied soul is no longer a soul). But must disembodied souls be matterless? There's reason to think that human souls have matter (in the Aristotelian sense of "matter") quite apart from their union with the body. For Aristotle, matter (hyle) is potentiality: a bronze sphere's matter is the bronze of which it consists, for the bronze is potentially the bronze sphere. Now, a human soul has the potential to think and the potential not to. (This is in contrast to an animal or plant soul, which simply is not in the intellectual ballpark.) Thus, both a thinking human soul and a non-thinking human soul have matter, namely a human soul: for a human soul is potentially a thinking human soul and also potentially a non-thinking human soul. If both a thinking human soul and a non-thinking human soul have matter, then a human soul always has matter—and this is true quite apart from the soul's union with the body. Therefore, the matter rule doesn't rule out the existence of disembodied human souls.
References:
Ackrill, J.L. 1987. A New Aristotle Reader. Princeton: Princeton UP.
Bos, A.P. 2003. The Soul and Its Instrumental Body: A Reinterpretation of Aristotle's Philosophy of Living Nature. Leiden: Brill.
Caston, Victor. 2006. "Aristotle's Psychology". In Mary Louise Gill and Pierre Pellegrin, eds. A Companion to Ancient Philosophy. Hoboken: Wiley-Blackwell.
Gerson, Lloyd. 2004. "The Unity of Intellect in Aristotle's De Anima". Phronesis 49 (4): 348-73.
Robinson, Timothy A. 1995. Aristotle in Outline. Indianapolis: Hackett.
Wedin, Michael V. 1993. "Tracking Aristotle's Noûs". In Michael Durrant, ed. Aristotle's De Anima in Focus. London: Routledge.
Witt, Charlotte. 1989. Substance and Essence in Aristotle: An Interpretation of Metaphysics VII-IX. Ithaca: Cornell UP.
[1] Charolette Witt (1989, 3) objects to identifying Aristotelian forms with properties. However, as far as I can tell, her objection rests on the claim that Aristotelian forms are particulars (cf. 1989, 4, 143, 176). Even if forms are particulars, this doesn't mean that they can't be properties. It's possible to claim that properties are particulars; that's the central claim of "trope" theories of properties.
[2] As we'll see during this discussion, a number of contemporary scholars reject the second and the third theses—and thus, by extension, the fourth.
[3] One Aristotelian scholar has argued against the first thesis. According to A.P. Bos (2003), Aristotle regards the soul not as the form of the visible body but, rather, as the form of a subtle, ethereal entity that uses the visible body as its instrument. As far as I know, Bos's interpretation hasn't gained many academic supporters.
On a largely unrelated note, there's some disagreement about whether Aristotle regards the soul as the body's only form; Aristotle's claim that the soul is "substance qua form of a natural body which has life potentially" (DA 412a19-20) is ambiguous on this point. Aquinas, with his "unicity of form" doctrine, thought that the human body consisted of formless matter plus a single unified form, the human soul. I'm fairly sure that Aquinas is wrong about this, but I won't argue that here.
[4] All quotations from Aristotle follow the translations in Ackrill 1987.
[5] Timothy Robinson appears to subscribe to a rather attenuated version of this interpretation. Robinson (1995, 49) suggests that the intellect is like "a little piece of prime matter" inside a person. "Prime matter" is the Aristotelian term for the basic stuff that (almost) everything is made of. Robinson's point seems to be that, just as a piece of prime matter has the potential to become any physical thing, so the intellect is a little nonphysical object that has the potential to become any thought.
[6] I'll admit that it wouldn't be the first case of inexplicable redundancy in Aristotle's writings.
[7] This argument is admittedly a bit loose. A critic might point out that, according to the passage just quoted, the "place of forms" is "not the whole soul but that which can think", and this can only be the intellect. Thus, it might seem, the passage merely affirms that (1) the intellect is part of the soul and (2) thinking involves receiving (intelligible) forms. If that's so, then the passage is compatible with an interpretation that regards the intellect as a property of the body (albeit a property not localized in any particular organ). I reply that, if such an interpretation were correct, then Aristotle wouldn't have said that the only the thinking part of the soul is a "place of forms". After all, according to Aristotle, sensation involves receiving sensible forms. So why doesn't Aristotle say that the sensitive part of the soul is also a "place of forms"? Here's the only answer that I can think of: Aristotle regards sensation as an activity of the living body (or "body-soul composite", if one prefers the more ambiguous expression), whereas he regards thinking as an activity of the soul itself. Only this answer seems to explain why the soul is a "place of forms" with regard to the thought but not with regard to sensation. If I'm right about this, then the intellect is a property of the soul itself, not of the ensouled body.
[8] Consider a mathematical analogy. Being a three-sided plane figure is not the same property as having internal angles that add up to 180 degrees. Yet the first property necessarily confers the second property upon an object.
[9] True, Aristotle says that not "all soul but [only] the reason" is separable from the body (Metaph. 1070a24-27). But does "reason" here mean the intellect alone, or does it mean the rational soul? If it means the rational soul, then Aristotle isn't saying that the intellect is the only part of the soul that can separate from the body: rather, he's drawing a distinction between irrational (i.e. plant and animal) souls, which aren't separable from the body, and rational (i.e. human) souls, which are separable.
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