The best way for the modern reader to approach this medieval commentary on an ancient text by Aristotle is to start by reading the ancient text—which is apparently a sequel to Aristotle’s On the Soul—on its own, outlining its structure, paraphrasing and summarizing, and noting any comments and questions that occur. The commentary can then be read with the greatest possible appreciation of its distinctive procedures and interests, in dramatic contrast to those of Aristotle. At that point, the reader with even slight familiarity with Aquinas’s work may wish to turn at once to his prologue (p. 14),...

As The Philosopher says in On the Soul III, “just as things are separable from matter, so also is what pertains to intellect”:¹ for everything is intelligible inasmuch as it is separable from matter. Hence what is by nature separate from matter is of its very self intelligible in actuality; but what is abstracted by us from conditions of matter is made intelligible in actuality by the light of our agent intellect. And because the habits of a power are specifically distinguished according to differentiation of that which is the per se object of the power, the habits of the...

436b8 Having presented a prologue in which he has shown his intention, here the Philosopher begins to follow up his proposal.

First he determines about what pertains to the external sense-power. Second he determines about certain things pertaining to inner sensitive cognition, namely memory and recollection, where he says About memory and remembering (449b4); for the treatise On memory and recollection is part of the present book according to the Greeks.²

On the first point he does three things. First he takes up some things that were said about the sense-power in the book On the soul and that are...

437a19 After The Philosopher has summarized what is necessary for the present consideration of sensitive powers themselves, now he proceeds to his principal proposal in this book by applying the consideration of sense-powers to what is bodily.

First with respect to sense-organs. Second with respect to sensible objects, where he says Concerning sensible objects (Chapter 5, 439a6).

On the first point he does two things. He assigns sense-organs to elements, first disproving arguments of others; second determining what might more probably be the case, where he says If, then, what happens in these cases (Chapter 4, 438b16).

On the first...

438a5 After the opinions of Plato and Empedocles, here, in the third place, The Philosopher follows up the opinion of Democritus.

On this point he does three things. First he shows what Democritus said correctly and what he said incorrectly. Second he follows up what he said incorrectly, where he says But it is inconsistent (438a10). Third he follows up what he said correctly, where he says For it is indeed true that sight is made of water (438a12).

Accordingly he first says that Democritus spoke correctly in assigning sight to water, but he spoke incorrectly in saying he thought...

438b2 After the Philosopher has disproved the opinion of those who hold that vision occurs by extromission, here he determines the truth.

On this point he does three things. First he makes clear how vision occurs according to his own thought. Second, on this basis, he gives the cause of something mentioned above concerning the organ of sight, where he says It is reasonable (438b5). Third he shows the cause by a sign, where he says This is also clear (438b11).

Accordingly he first takes up something that was said in the book On the Soul, that it is impossible...

439a6 After The Philosopher has applied the consideration about sense-powers of animals to sense-organs, here he applies it to sensible objects themselves.

First he states his intention. Second he carries out his proposal, where he says Accordingly, as was said about light (439a18).

On the first point he does two things. First he proposes his intention. Second he clarifies what he said, where he says Each, then, is spoken of in two ways (439a12).

Accordingly he first speaks of proper sensible objects, those perceived in relation to each sensitive part, that is, each individual sense-organ, which he says to distinguish...

439b14 After the Philosopher has shown what color is, here he proceeds to distinguish the species of colors.

First with respect to extreme colors; second with respect to intermediate colors, where he says But we must speak about the other colors (439b18).

Now the differences by which species are distinguished should divide a genus per se, not accidentally, as is clear in Metaphysics VII.¹ Therefore, he concludes to the variety of species of color from the very nature of color, which he explained through the definition given above.

It is established from the foregoing that the subject of color is...

440a15 Having presented two ways of generation of intermediate colors, here he compares the ways mentioned to one another.

On this point he does three things. First he eliminates a position from which one of the ways mentioned followed. Second he compares the ways mentioned to one another, where he says Accordingly, in the position that bodies are juxtaposed (440a20). Third he shows how far each of the ways mentioned can be maintained, where he says Therefore if it cannot be that any magnitude is invisible (440a26).

Accordingly he first says that the Ancients held that color is nothing but...

440b28 After the Philosopher has determined about color, here he next determines about flavor.

First he says what his intention is about. Second he carries out the proposal, where he says The nature of water (441a3).

Accordingly he first says that after color odor and flavor must be discussed.

On this point he gives the cause of two things.

The first is why these should be treated in conjunction, namely because of their association, for the two are almost the same affection. He calls each of them an “affection” because both are in the third species of quality, which is...

441a30 After the Philosopher has eliminated opinions of others on the cause of the origin of flavors, here he gives the true cause according to his own opinion.

On this point he does three things. First he gives the cause of the generation of flavors. Second he defines flavor, where he says And this is flavor (441b19). Third he clarifies something he said, where he says Now we must take it that flavors are affections (441b23).

On the first point he does three things. First he shows that flavors pertain to earth, and not only, as the Ancients held, water....

442a12 After the Philosopher has determined the generation of flavor, here he distinguishes species of flavors.

On this point he does three things. First he shows the generation of intermediate flavors in general. Second he shows how intermediate flavors are diversified, where he says And these are also according to proportions (442a13). Third he shows how sweet and bitter are related to one another, where he says As black is privation of white (442a25).

Accordingly he first says that as intermediate colors are generated from mixture of white and black, so intermediate flavors are generated from mixture of sweet and...

442b27 After the Philosopher has made a determination about flavors, here he begins to make a determination about odors.

This is divided into two parts. In the first he makes the determination about odors. In the second he compares the sense of smell to the other senses, where he says The senses exist in an odd number (Chapter 13, 445a4).

On the first point he does two things. First he determines the generation and the nature of odor. Second he determines the species of odor, where he says There are two species of the odorous (Chapter 12, 443b17).

On the...

443b17 After the Philosopher has determined the generation and nature of odor, here he determines the species of odors.

On this point he does two things. First he determines the various species of odor. Second he determines the modes of smelling, where he says For this reason (444a19).

On the first point he does three things. First he proposes that there are species of odor. Second he determines the species of odor by correspondence with species of flavor, where he says One kind of odor (443b19). Third he determines the species belonging to odor of itself, where he says But...

444b7 After the Philosopher has shown that men and certain other animals smell by breathing, here he inquires into the way non-breathing animals smell.

On this point he does two things. First he shows what is clear in such animals; second what is unclear, where he says But what they sense it with (444b15).

Accordingly he first says that it is clear that animals that do not breathe sense the odorous, because, as we see, fish and the whole class of insects—that is, partitioned animals such as ants, bees, and the like—acutely sense their nourishment from a distance,...

445b3 After the Philosopher has determined about sense-organs and sensible objects, here he determines some questions about the sense-power and sensible objects.

First he raises a question about sensible objects themselves. Second he raises another about alteration of the sense-power by a sensible object, where he says But someone will raise an objection (Ch.15, 446a20). Third he raises a third about the sense-power itself, where he says But there is also another such objection (Ch.16, 447a12).

On the first point he does three things. First he raises the question. Second he introduces arguments about it, where he says But this...

446a20 After the Philosopher has followed up the first question, which concerns sensible things themselves, here he proceeds to the second question, which concerns the alteration of the sense-power by sensible objects.

On this point he does three things. First he raises the question. Second he argues it, where he says Empedocles says (446a26). Third he solves it, where he says On the other hand (446b13).

On the first point it must be considered that, as was established above, some held that a sense-power is changed by sensible things by way of an emanation, so that it is the sensible...

447a12 Having solved two questions, here the Philosopher follows up the third, which is from the point of view of the sense-power itself.

On this point he does three things. First he raises the question. Second he argues for the false position where he says If a greater movement (447a14). Third he determines the truth where he says With respect to the objection (Ch.18, 448b17).

Accordingly he first says that concerning the senses themselves there is another such objection raised, namely whether it can happen that two senses sense simultaneously and at the same indivisible point of time, for instance...

448a1 Having presented two arguments to show that it is impossible for two senses to sense simultaneously, here he presents a third argument for the same conclusion based on the contrariety of sensible objects.

He says that alterations caused by contraries are contrary, for instance heating and cooling. But contraries cannot simultaneously be in the same “atomon”—that is, the same indivisible part (contraries can simultaneously be in the same divisible part with respect to different parts of it). But it is clear that objects under one sense-power are contraries, for instance sweet and bitter. Therefore they cannot be sensed...

448b17 After the Philosopher has eliminated a false solution, here he seeks the true one.

On this point he does three things. First he investigates the truth about the aforementioned question. Second he proves something he presupposed in the foregoing, where he says Now it is clear that everything that is sensible (449a20). Third he adds an epilogue to what was said in this book, where he says Something has been said, then (449b1).

On the first point he does two things. First he proposes what he intends. Second he carries out the proposal, where he says First, then, whether...

The occasion for the original draft of this introduction was a conference on Aristotle and Islamic philosophy in honor of Father Joseph Owens’s seventy-fifth birthday. For such a commemorative event it seemed not inappropriate, for three reasons, to focus on Thomas Aquinas’s Exposition on Aristotle’s treatise De memoria et reminiscentia.

In the first place, when this paper was originally delivered, Father Owens was present in the audience. Yet it would seem that that was impossible. For, as Aristotle explicitly states,

. . . memory is of what came to be: no one will say that the present is being remembered...

As the Philosopher says in the seventh book on the Histories of Animals,⁶ nature proceeds from inanimate to animate things little by little, so that the genus of inanimate things comes before the genus of plants. For plants, when compared to other bodies, seem to be animate, even though when they are compared to the genus of animals they seem to be inanimate. In the same way, nature proceeds from plants to animals in a continuous order; for certain immobile animals—those that adhere to the earth—seem to differ little from plants. So, too, in the order of progression...

449b30 After the Philosopher shows what memory is, he goes on to show to what part of the soul it belongs.

He does two things in this regard. First he presents what is needed for explaining what he has set out to do. Second he explains the thing he set out to do, where he says It is necessary, however, to know (450a9).

Concerning the first of these topics he does three things. First he sets out his intention. Second, by using an example, he explains what he has said, where he says For the same affection occurs (450a1). Third,...

450a25 After the Philosopher shows what memory is, and to what part of the soul it belongs, here he shows the cause of remembering.

In this regard he does two things. First he presents a difficulty.² Second he resolves it, where he says Or is it the case (450b20).

With respect to the first point he does three things: first he raises thedifficulty; second, he makes one of its presuppositions explicit, where he says For it is clear (450a27); third he brings up the arguments bearing on the question, where he says But if such is the case (450b11).

Accordingly...

451a18 After the Philosopher has settled his determination on memory and remembering, he turns to the topic of recollecting.

First he states the object of his interest; second he pursues the goal set out, where he says For recollection is neither (451a20).

Accordingly, first he says that after he has spoken¹ about remembering it remains for us to talk about recollecting, in order that whatever truths might be taken up by means of the dialectical discussions may first be supposed as being true. In this way he excuses himself from a long disputation about things pertaining to recollection.²

451a20 Then,...

451b10 After the Philosopher has inquired into how recollection is related to the other things that pertain to cognition, here he begins to explain the manner in which recollecting takes place.

First he explains the manner of recollecting. Second he points to the difference between memory and recollection where he says Now, then, that those with good memories (Ch.8, 453a4).

Concerning the first topic he does two things. He shows how recollecting takes place first with regard to the things one remembers; and second with regard to the time (for recollection is concerned with time, just as memory is), where...

452a4 After the Philosopher shows how recollecting takes place, here he explains two points that were touched upon above.¹

In the first place, he shows how recollecting differs from relearning. Second² he shows that one who recollects must begin from starting-points, where he says A beginning-point (452a12).

With respect to the first topic he does two things. First he shows how recollecting differs from relearning. Second³ he shows how recollecting differs from rediscovering, where he says Often, however, one cannot any longer recollect (452a7).

With respect to the first point, we must bear in mind that both he who recollects...

452b7 After the Philosopher has shown the mode of recalling from the side of the things to be recalled, here he determines the mode of recalling from the side of time.

And first he sets out what he intends to do. Second he clarifies what he had set out, where he says There is, however, something by which one judges (452b8).

He says first, therefore, that in recollecting it is most necessary to know time, namely the past, which memory is concerned with, which recollection is a search for; past time is known by one who is recollecting sometimes under...

453a4 After the Philosopher has shown how recollecting takes place, he now shows the difference between memory and recollection.

He refers to three differences. The first of these stems from one’s aptitude for each of the other two. For it was said above² that the same men are not good rememberers and good recollectors. The second difference stems from time, since recollection, because it is a path to memory, precedes it in time, as is apparent from what has been said already.³ The third difference stems from the subject in which each of them can be found. For many other...