The Plausibility of St. Thomas' Interpretation of De Anima III.5

One of the most interesting and difficult to interpret texts in the entire Aristotelian corpus is his very brief fifth chapter of De Anima III. In this chapter Aristotle speaks of an active or agent intellect as distinct from a passive one and argues that it alone is “immortable and eternal” along with a number of other attributes. The nature of this active intellect has been subject to much debate. On the one hand, Thomas Aquinas argued that the active intellect was a power of each individual human soul required for abstraction. Others have argued that there is only one active intellect and some even claim that this intellect is the divine intellect itself. In this paper we will examine Aristotle’s passage and then compare the strengths and weaknesses of Aquinas’ interpretation against the interpretation that the active intellect is the divine intellect and show that while Aquinas’ interpretation has implausible elements, his main thesis is defensible.

Before looking at interpretations, we can briefly look at the passage itself and summarize it and note some of the areas of controversy. Aristotle begins III.5 by noting that in every class of objects, there is both matter and a productive cause, so too is there this active and potential element “in the soul”. “Since in every class of objects, just as in the whole of nature, there is something which is their matter, i.e., which is potentially all the individuals and something else which is their cause or agent in that it makes them all–the two being related as an art to its material–these distinct elements must be present in the soul also.” The phrase “in the soul” will be a matter of controversy as Aristotle seems to be talking about an active and potential principle in each soul as Aquinas will argue but others will read this differently as we will see.

Aristotle then explicitly distinguishes between two senses of mind, an active and passive sense. “Mind in the passive sense is such because it becomes all things, but mind has another aspect in that it makes all things; this is a kind of positive state like light; for in a sense light makes potential into actual colors.” Aristotle repeats a saying he has already made in the De Anima, namely, that mind is potentially all things because it thinks all things. That is, since there is a kind of identity between something known and the mind and the mind can think of everything, the mind can potentially be all things in some sense. Aristotle then uses an analogy of light to explain the active intellect by saying it “makes all things” in the way in which light makes potential color actual. It again seems prima facie that Aristotle is speaking of each soul up until this point. Defenders of the divine intellect theory will try to downplay the light analogy. However, what immediately follows this sentence makes their view more plausible.

Aristotle then claims that the active intellect has a number of attributes. “Mind in this sense is separable, impassive, and unmixed, since it is essentially an activity; for the agent is always superior to the patient, and the originating cause to the matter.” Of these attributes, being “essentially an activity” is the most important for the debate under discussion. The Greek says, “τῇ οὐσίᾳ ὤν ἐνεργεία” which could be rendered “being actuality with respect to its substance/being”. Something whose being is actuality does sound more like Aristotle’s God of Metaphysics XII rather than a part of a human soul though we will see how Aquinas handles the passage below.

Aristotle then makes a distinction between actual and potential knowledge. “Actual knowledge is identical with its object. Potential is prior in time to actual knowledge in the individual, but in general it is not prior in time. Mind does not think intermittently.” Here Aristotle teases out more his notion of identity between thought and reality. In act, there is an identity between knowledge and its object which, in the individual, was there only potentially beforehand. However, the active mind (presumably) thinks in a continuous fashion rather than intermittently and so in general there is no distinction in time between potential and actual knowledge.

Aristotle then closes the passage with his famous line about the immortality of the active intellect. “When isolated it is its true self and nothing more, and this alone is immortal and everlasting (we do not remember because, while mind in this sense cannot be acted upon, mind in the passive sense is perishable) and without this nothing thinks.” The comments about remembering are a bit mysterious. It could be that Aristotle is referring to a time after death after the immortal active intellect has left the body. Caston argues for a different punctuation and translation so that the passage reads, “We do not remember that while this cannot be affected, the intellect that can be affected is perishable”. The final “this” is also unclear as it could refer to the mind as a whole or to the active intellect alone.

Having looked at the passage it is clear that there are some ambiguities in the text and that certain parts of the passage are open to debate. We will then look more closely at two competing interpretations, that of Thomas Aquinas and that of Victor Caston and see if Aquinas’ position or a slightly modified version of it is defensible.

Aquinas begins by noting that the active intellect or what he calls the agent intellect (Lat. intellectus agens) is needed for abstraction. “[B]ecause Aristotle asserts that whatnesses of sensible realities exist in matter and are not intelligible in act, he had to assert that there is some intellect that abstracts them from matter and thus makes them intelligible in act” As James T.H. Martin has argued, Aquinas is reasoning as follows:

1. Intelligibility requires separation from matter

2. The forms of sensible things are not separate from matter

3. Therefore the forms of sensible things are not themselves separate from matter but rather are in matter and not actually intelligible.

The active intellect then is required for making sensible forms intelligible in the mind and impressing them on the passive intellect.

Next Aquinas’ translator renders “τῇ οὐσίᾳ ὤν ἐνεργεία” as substantia actus ens, a substance being in act. Aquinas however interprets this as follows. He says the agent intellect, “is in act according to its own substance, and in this it differs from the potential intellect, which is in potency according to its own substance, but is in act only insofar as it has received a species” Caston argues that this attribute is evidence that the agent intellect is the unmoved mover of Metaphysics XII who is pure act. Aquinas’ argument for his position works well if the assumption is that Aristotle is discussing human knowledge. He points out that if the active intellect were a separate substance, that would leave human nature incomplete. Moreover, he returns to Aristotle’s analogy of light and notes that the active intellect is in act in the way light is, i.e. always able to make possible color actual.

Therefore, it is related as to the intelligible objects as an act insofar as it is a certain immaterial active power capable of making other things like itself—that is, making them immaterial; and in this way things that are potentially intelligible it makes actually intelligible. For so too does light make colors actual, but it does not have within itself the determination of all the colors. But this active power is a certain participation in the intellectual light of separated substances, so the Philosopher compares it to a habit, or a light, which would not be an appropriate way of describing it if it were itself a separate substance

Aquinas’ arguments here then depend on the prior point about the context of De Anima III.5, i.e. whether Aristotle is talking about human understanding or not.

In terms of the active intellect being immortal and impassible, Aquinas takes Aristotle to be referring to the mind as a whole surviving death and must make another controversial exegetical move by identifying the passive intellect that Aristotle says is corruptible as a part of the soul connected with the passions. “But the passive intellect—that is, the part of the soul that is subject to the passions mentioned—is corruptible, for it pertains to the sensitive part. Nevertheless, this part of the soul is called an “intellect” just as it is also called “rational”: inasmuch as it in some way participates in reason by being obedient to reason, and by following its movement, as is said in the Ethics.”

This move is particularly controversial since Aristotle had just discussed the passive intellect in De Anima III.4. In 429a24, Aristotle says, “That part of the soul, then, which we call mind (by mind I mean that part by which the soul thinks and forms judgements) has no actual existence until it thinks”. It is not obvious that the passive intellect in III.5 is entirely different from this intellect in III.4 and is merely something attached to the passions. This difficulty notwithstanding, it would show perhaps that Aristotle thought that part of the mind survived death but not the whole mind which, while not Aquinas’ view, is similar to it.

Unfortunately, in his commentary on De Anima III.5, Aquinas does not argue against the very position that Caston takes up which will make weighing their arguments more difficult. Victor Caston’s proposed interpretation of De Anima III.5 is that the active intellect in question and the whole passage have nothing to do with the human soul but is rather a brief exposition of the divine similar to Aristotle’s excursuses into the divine in e.g. Metaphysics XII, Physics VIII, and Ethics X. We have already seen some of what Caston has said in response to Aquinas’ interpretation so we can look at a few strengths and weaknesses of his view and then assess it against that of Aquinas.

Of first importance is the context of De Anima III.5. Aquinas, following the face value of the text thinks of Aristotle as speaking of faculties “in the soul” since Aristotle says at 430a13 that the active and passive principles must be ἐν τῇ ψυχῇ. Caston argues that this phrase is open to a wider set of meanings and points out that Aristotle lists eight meanings of “in” in Physics 4.3. If we limit our search to within the De Anima, Aristotle uses that exact prepositional phrase five times in total including in III.5. In 410a7, 410a12, and 432a1 Aristotle is clearly referring to individual human souls when he says that elements cannot exist in the soul or that stone is not in the soul. Similarly, in 431b6 Aristotle is speaking about an individual man perceiving. Thus, given his usage of that phrase within the work, Aquinas’ view seems more plausible since it matches Aristotle’s other uses of the phrase.

A second major issue of contention between Caston and Aquinas is whether there is any need for an active intellect. While Caston admits there are gaps in Aristotle’s account of the soul, he thinks it would be “bizarre” for Aristotle to address the supposed gap that Aquinas claims exists in the way he does so shortly in III.5. He notes, Caston argues, “For the appeal to a second intellect becomes a deus ex machina. It suggests that Aristotle was aware of a significant gap in his psychology and yet did not care to address it except in this cursory way, by invoking a magical problem solver – something which is certainly not very charitable, if indeed it is credible at all”

Here arguments for each side get tricky. To simply assert that there was no gap to be solved begs the very question since it would rule out Aristotle explaining a gap in his account from the outset. In other words, if I think prior to De Anima III.5 that Aristotle has no issue explaining abstraction, then I could always assert that whatever is said in III.5 can’t be explaining a gap because no gap exists. Such an approach would not properly be open to the text of Aristotle. Nonetheless, it is certainly true that III.5 is brief considering its content. However, such brevity is not unique to De Anima III.5 and is not a decisive argument against Aquinas’ reading. It seems Caston’s main motivation for reading the active intellect as the divine is that, “we needn’t go on a wild goose chase trying to invent a role for the so-called Agent Intellect to play in human psychology”. Simplicity is certainly a virtue but if “in the soul” means in each particular soul, then regardless of what Caston thinks about Aristotle’s views up to that point or his brevity or use of an analogy, Aristotle can in his own way be talking about faculties of the individual soul.

Moreover, it would seem that the brevity of the passage would cut against Caston’s view as well. If he were discussing God’s mind, one would reasonably expect more than a paragraph and some explicit mention of God somewhere in the text. Arguments regarding brevity and simplicity ultimately cannot decide this interpretive debate.

Martin too critiques Aquinas regarding his view of active intellect and says that his interpretation of the active intellect is “not plausible” and cannot be inferred from Aristotle’s writings. Martin argues that Aquinas is referencing a passage in Aristotle’s Metaphysics I when he says, “Aristotle asserts that whatnesses of sensible realities exist in matter and are not intelligible in act”. However, the passage Martin thinks Aquinas is referring to regards only Aristotle’s argument against Platonic forms and would thus render Aquinas’ argument which we laid out above to be invalid because of an equivocation of the word “separate”.

Aquinas never says however that he is referring to the Metaphysics. At face value then, we can interpret Aquinas as holding that it is precisely in De Anima III.5 that Aristotle holds that position rather than somewhere else in his corpus. To Martin’s point it is true that Aristotle nowhere says something like “the forms of sensible things are not themselves separate from matter and thus not actually intelligible.” However, Aristotle clearly affirms (and Martin agrees) the separability of form from matter in the passage immediately preceding III.5 (4030a7-8). Second, Aristotle can plausibly be read as saying this in III.5 when he says that active mind “makes all things”. Aquinas is not equivocating in his argument when he notes that sensible forms need to be separate from matter to be intelligible and that the active mind is needed for this separation.

In some support of Aquinas, Ruth Reyna on the other hand does think that something is incomplete with Aristotle’s account until III.5 and that the discussion of the agent intellect does explain how the intellect is separable, something anticipated earlier in the text. Cohoe also notes that Aristotle’s earlier anticipations of the separability of body and soul lend support to Aquinas’ interpretation of this passage. Overall, Aquinas’ argument about the need for the agent intellect in abstraction seems plausible notwithstanding Aristotle’s brevity on such an important topic.

One of Caston’s other objections which lands the hardest is the fact that the active intellect is imperishable and the passive perishable. This means that these two cannot be the same thing. This, as we noted earlier is probably the weakest point in Aquinas’ exegesis for he has to take the implausible route of distinguishing the intellect of De Anima III.4 from the passive intellect of III.5. However, while there is clearly a real distinction between the passive and active intellect, it is not impossible to hold that these are simply two separable parts of the intellect. While that would be a strange view, the separability of the intellect is a unique thing and the fact that part of the soul can exist without the body while part cannot, while strange, is not itself sufficient to discount the view as Aristotle’s.

We have seen that when comparing Thomas Aquinas’ reading of Aristotle to an alternative view put forth by Victor Caston, Aquinas’ view is a more plausible interpretation of Aristotle’s text. Aristotle’s passage in De Anima III.5 is short and difficult to interpret. However, if “in the soul” is taken in a straightforward way as it is in the rest of the work, Aquinas’ reading is very plausible with the one exception being his somewhat ad hoc qualification that the perishable passive intellect in III.5 is not really the mind at all but simply related to the mind because the passions are controlled by reason. Caston’s view of the active intellect being the divine mind has some pieces of evidence in its favor but is as a whole a less plausible reading of the passage than Aquinas’ view regarding the active intellect’s role in abstraction. Aquinas’ reading

is then helpful in our understanding of the role of the intellect in abstraction according to Aristotle.

Aquinas, Thomas. Commentary on De Anima at aquinas.cc

Aristotle. On the Soul. trans. W.S. Hett, Cambridge: Harvard University Press, 1936.

Caston, Victor. “Aristotle’s Two Intellects: A Modest Proposal.” Phronesis 44, no. 3 (1999): 199–227.

Cohoe, Caleb Murray. “Nous in Aristotle’s De Anima.” Philosophy Compass, 9/9 (2014): 594–604.

Martin, James T.H. “Aquinas as a Commentator on De Anima 3.5” The Thomist: A Speculative Quarterly Review 57, no. 4, (1993): 621-640. at projectmuse.com

Reyna, Ruth. “On the Soul: A Philosophical Exploration of the Active Intellect in Averroes, Aristotle, and Aquinas” The Thomist: A Speculative Quarterly Review, 36, no. 1, 1972, 131-149 at projectmuse.com