Lecture 18 — How simultaneous sensation is possible

With respect to the objection stated above, it must be considered whether it is possible or not possible to sense several things simultaneously. By “simultaneously” I mean together in one indivisible moment of time.

First, then, whether it is possible to sense simultaneously by means of a different part of the soul, which is not indivisible, but is indivisible in the way that something continuous is.

Or first, the case of objects sensed by one sense. For instance, if sight senses different colors with different parts of itself, it will have several parts specifically the same, for what is sensed belongs to the same genus.

If someone says that, since there are two eyes, nothing prevents it from being like this in the soul as well—it must be said that perhaps out of these some one thing is made, and they have one operation. But in the other case, if some one thing is made out of two, that will be what senses; but if they are separate, it will not be like the other case.

Moreover, there will also be several senses that are the same, as if someone were to speak of sciences that are not different. For there can be neither an operation without its own power, nor a sense power without the former.

But if it senses this by one indivisible part, it is clear that it also senses the others. For it is more possible for several of these to be sensed simultaneously than ones of different genera. If, then, the soul senses sweet by one part but white by another, out of these either some one thing is made or it is not. But it necessarily is, for the sensitive part is some one part.

What one object, then, does it have? For there is no one object made out of these objects. Therefore there is necessarily some one part of the soul by which it senses everything, as was said before, but it senses different genera by means of different parts.

Accordingly, inasmuch as it is indivisible it is one power in actuality able to sense sweet and white. But when it is made divisible, it is different in actuality.

Or again, as it is in things themselves, so also in the soul. For one and numerically the same thing is white, and sweet, and many other things, if the affections are not separable from one another. But the being (esse) of each is different. Similarly, then, we should posit that also in the soul the power that is able to sense all things—although these differ in being, some in genus and some in species—is one and numerically the same. Hence it will also perceive by means of what is simultaneously one and the same, but not the same in aspect (ratio).

Now it is clear that everything that is sensible is a magnitude, and what is indivisible is not sensible. For there is an infinite distance from which it will not be able to be seen, but that from which it can be seen is finite. And it is similar with the audible and the odorous, and whatever senses without touching the things themselves. And so there is a limit to the distance from which it cannot be seen, and a point from which it can first be seen. And so there is necessarily something indivisible beyond which there is no sensing, but on this side of which there is necessarily sensing. If, then, something indivisible is sensible, when it is placed at the limit that is the last point from which it is not sensible and the first point from which it is sensible, it will simultaneously be visible and invisible. But this is impossible.

Something has been said, then, about the sensitive parts, and sensible objects, how they are related, both in general and with respect to each sensitive part. Of what remains, the first to be considered are memory and recollection and sleep.

281. With respect to the objection stated above (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; [294]).

Third, he adds an epilogue to what was said in this book, where he says something has been said, then (449b1;[297]).

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 it is possible to sense simultaneously (448b20; [282]).

Accordingly, on the basis of the fact that what some have said has been eliminated (Cf. ch. 17, nn. 278–80.)—namely that several things are sensed simultaneously not in a moment of time that is indivisible according to the truth of the matter, but in a length of time that is imperceptible because of brevity—we must consider, with respect to the objection raised above, (Cf. ch. 16–17, nn. 253–68.) whether it is or is not possible to sense several things simultaneously, taking simultaneously to mean in an indivisible moment of time.

282. Then when he says first, then, whether it is possible to sense simultaneously (448b20), presupposing that an animal does sense different sensible objects simultaneously—for we obviously have experience of this—he investigates how this is possible. On this point, he does three things.

First, he presents a false way.

Second, he disproves it, where he says or first, the case of objects sensed by one sense (448b22; [283]).

Third, he presents the true way, where he says accordingly, inasmuch as it is indivisible (449a10; [288]).

Accordingly, he first says that it must first be considered whether it is possible to simultaneously sense different sensible objects by means of a different part of the soul, the sensitive part of the soul being, as it were, not indivisible—that is, not incapable of being divided—although it is indivisible in the sense that it is not divided in actuality, being like a continuous whole. For if we understand the sensitive part of the soul to be like a continuum, the arguments presented above are dissolved, because nothing will prevent different and contrary things from being in the sensitive power of the soul with respect to its different parts, in the way we see that one body is white in one part and black in another.

283. Then when he says or first, the case of objects sensed by one sense (448b22), he disproves the way just mentioned. On this point, he does three things.

First, he shows that it will follow that even one sense, for instance sight, is divisible into several parts.

Second, he shows that this is impossible, where he says if someone says (448b26; [284]).

Third, he shows that it is also not possible with respect to different senses, where he says but if it senses this by one indivisible part (449a2; [286]).

Accordingly, he first says that since one can simultaneously sense several objects by the same sense, as when sight distinguishes between white and black, according to the foregoing argument one will have to say that it senses the different colors by different parts of itself, and so it will follow that the same sense will have several parts specifically the same. For it cannot be said that parts of the sense of sight differ specifically, because everything sensed by sight belongs to the same genus, and there is specific difference among sensitive powers only because of different genera of sensible objects.

284. Then when he says if someone says (448b26), he disproves what was said by two arguments.

The first is that if someone says that, just as there are two organs of sight—that is, two eyes—nothing prevents there being two senses of sight in the sensitive soul as well, in response to this it must be said that out of the two eyes some one thing is made, and that there is one operation of both eyes—that is, inasmuch as the seeings of the two eyes concur, by way of certain nerves, at an inner organ of sight that is near the brain, as was said above. (Cf. ch. 4, n. 64.) But if, likewise, in the soul some one thing is made out of two powers of sight by the two powers concurring in some one principle, it is to that one principle that the operation of sensing will be attributed. But if the two powers of sight are altogether separate in the soul because they do not concur in some one principle, the relation of powers of sight in the soul will not be like that of eyes in the body, and so the comparison was not suitable for showing what was proposed. Therefore, it does not seem reasonable to say that there are two powers of sight in the soul.

285. He presents the second argument where he says moreover, there will also be several senses (448b29). He says that according to the position stated above there will be several senses that are specifically the same, for instance several senses of sight or several senses of hearing. It would be as if someone said that there are, in the same human being, several sciences that are not specifically different, for instance several grammars or several geometries. It is certainly possible for there to be numerically several grammars or several powers of sight in different human beings, but not in one and the same human being, just as it is impossible for there to be numerically several whitenesses in one and the same subject.

To show that there cannot be several senses specifically the same in the same human being, he adds that sensitive power and operation follow from one another in such a way that neither can there be a power without its proper and per se operation, nor an operation without its proper power. But sensitive operation is distinguished according to sensible objects, and so where sensible objects are completely the same, there are not different sensitive powers causing different operations. The habits of the sciences are similar: their acts are distinguished according to their objects.

286. Then when he says but if it senses this by one indivisible part (449a2), he shows that this is impossible for objects of different senses, that is, that it is impossible for them to be sensed by different parts of the soul.

He says that if sensible objects belonging to different genera are perceived by some one and the same indivisible part of the soul, it is clear that much more so are the others, that is, those belonging to one genus. For it was proved above that it is more possible for objects belonging to one genus to be sensed simultaneously than objects belonging to different genera, and this is especially true with respect to the identity of the one perceiving. (Cf. ch. 16, nn. 258–64.)

He proves as follows that the soul does perceive sensible objects of different genera by the same indivisible part. If the soul senses sweet by one part of itself and white by another, out of these two parts either some one thing will be made or it will not. But one must necessarily say that there is some one thing to which all these parts—that is, the different senses—are referred, because the sensitive part is some one part of the soul. But it cannot be said that the sensitive part of the soul has some **one **genus of sensible objects—unless, perhaps, it were said that out of all objects of particular senses—for instance color, sound, and other such objects—is made one sensible object that would correspond to the one part of the sensitive part that is common to all proper senses. But this is impossible. Therefore there is necessarily some one part of the soul by which an animal senses everything, but it senses different genera by means of different parts, for instance color by sight, and sound by hearing, and so on.

287. Now here it must be considered that wherever there are different ordered powers, a lower power is related to a higher one as an instrument, because the higher moves the lower, and action is attributed to the principal agent acting by means of an instrument, as we say that a builder cuts by means of a saw. It is in this way that the Philosopher says here that the common sense perceives by means of sight, and by means of hearing, and by means of other proper senses, which are different potential parts of the soul, and not, as was claimed above, like different parts of a continuum.

288. Then, when he says accordingly, inasmuch as it is indivisible (449a10), he shows how the same indivisible part of the soul can simultaneously perceive different things. He presents two ways.

He presents the first briefly and obscurely, because it has been presented more fully in On the Soul. (Aristotle, On the Soul 3.2, 427a7–9; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 27, nn. 599–614; lect. 6, nn. 773–76.) For evidence on this point, then, it must be considered that, since the operations of the proper senses are referred to the common sense as their first and common principle, the common sense is related to the proper senses and their operations in the way that one point is related to different lines that meet in it. Now a point that is the terminus of different lines is, considered in itself, one and indivisible, and in this way the common sense, inasmuch as it is in itself indivisible, is one power in actuality, able to sense sweet and white, sweet by means of taste, and white by means of sight. But if the point is considered separately insofar as it is the terminus of this line, and separately again insofar as it is the terminus of another line, it is thus in a way divisible, because we take the one point as two. Likewise the common sense, when it is taken as something divisible—for instance when it separately judges of white, and separately again of sweet—is different in actuality. But inasmuch as it is one, it judges differences among sensible objects. By this the arguments introduced above are dissolved, (Cf. cc. 16–17, nn. 254–68.) inasmuch as what senses different sensible objects is in a way one, and in a way not one.

289. He presents the second way where he says or again, as it is in things themselves (449a13). He says that as it is in external things, so, it can be said, it is in the soul. For we see that one and numerically the same body is white, and sweet, and many other such things that are predicated of it as accidents—that is, if such affections are not separated from one another, as happens when a body keeps its whiteness and loses its sweetness. But as long as the affections are not thus separated, the white thing and the sweet thing remain the same in subject, but differ in being. Likewise, it can be posited of the soul that the power able to sense all sensible objects—both those that differ in genus, such as white and sweet, and those that differ in species, such as white and black—is one and the same in subject. And according to this, it will have to be said that the soul senses different sensible objects by means of what in a way is one and the same, that is, one and the same in subject, but in a way is not the same, inasmuch as it differs in aspect.

Difficulties

I

290. Now an objection to this might be raised. For in what is outside the soul, although the same thing could be sweet and white, nevertheless the same thing cannot be white and black. Thus it would seem that the soul cannot simultaneously sense sensible objects of one genus when they are contraries.

291. Aristotle raises this objection in On the Soul when he says, and it is impossible for white and black to be simultaneous: therefore, neither can their species be experienced simultaneously. (Aristotle, On the Soul 3.2, 427a9–14; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 27, nn. 606–14.)

He suggests the solution by what he adds: if sense and intellect are similar. (Aristotle, On the Soul 3.2, 427a9.) By this he gives us to understand that the situation in sense and intellect is not completely similar to that in natural bodies. For a natural body receives forms according to their natural and material being, according to which they have contrariety, which is why the same body cannot simultaneously receive whiteness and blackness. But sense and intellect receive the forms of things spiritually and immaterially according to an intentional being, in such a way that they have no contrariety. Hence sense and intellect can simultaneously receive species of contrary sensible objects. Something like this can be seen in the transparent, which in one and the same part of itself can be altered by white and by black, because the alteration is not material or according to natural being, as was said above. (Cf. ch. 7, nn. 115–17.)

292. There is also something else to be considered: that sense and intellect not only receive the forms of things, but also make a judgment about them. Now judgment about contraries is not itself contrary, but something one and the same, because by one of the contraries a judgment is taken about the other. To this extent, what was said above is true, (Cf. ch. 16, nn. 258–64; ch. 18, n. 286.) that sensible objects belonging to one genus, where judgment about one of the objects is made by means of the other, can more readily be sensed simultaneously than objects of different senses.

II

293. But there is also another difficulty on this point, because the Philosopher’s words presented above (449a13–20) seem to confirm an opinion of the Stoics, who held that color and odor and other sensible objects are not sensed by different powers; and that there are not different sense powers; but that the soul itself, of itself, knows all sensible objects, and in doing so differs only in aspect.

To this it must be said that the solution of this second difficulty presupposes the first solution. Thus it must be understood that the soul—that is, the common sense, existing as numerically one, and differing only in aspect—knows different genera of sensible objects, which, however, are referred to it by the different powers of the proper senses.

294. Then, when he says now it is clear that everything that is sensible (449a20), he proves something he presupposed above, namely that nothing is perceived unless it is of some size. (Cf. ch. 14, n. 210.) He says that it is clear that everything that is sensible is a magnitude, and nothing indivisible is sensible. To prove this, he introduces the consideration that there is a distance from which a thing cannot be seen; he says that this distance is “infinite,” because if the distance is extended to infinity, nothing is seen from there. And there is a distance from which a thing can be seen, and this is “finite,” because a thing begins to be seen from a finite distance. It is similar with the other senses, namely hearing and smell, that sense from some distance through an external medium without touching the sensible things themselves.

295. Therefore, since the distance from which a thing cannot be seen is infinite in the direction away from sight, but finite in the direction towards sight, it follows that it is possible to identify a limit from which nothing is seen. But the distance from which a thing can be seen is finite in both directions. Therefore it is possible to identify a terminus from which a thing can first be seen. But anything intermediate between two quantities continuous with one another is indivisible. Therefore there is necessarily some indivisible point beyond which nothing can be sensed, and on this side of which a thing necessarily can be sensed. Therefore, if something indivisible is sensible, and it is placed at that indivisible boundary, it will follow that it is simultaneously visible and invisible: invisible inasmuch as it is at the boundary of the distance of the invisible, but visible inasmuch as it is at the boundary of the visible. But this is impossible. Therefore the first premise, that something indivisible is sensible, is also impossible. For if something indivisible is placed at the above-mentioned terminus, it will be partly seen and partly not seen, which cannot be said of the indivisible.

296. Now this proof might seem to fail, because it is not possible to identify a boundary from which all visible things begin to be seen: rather, bigger things are seen from a bigger distance, and smaller ones from a smaller distance.

To this it must be said that every sensible object is visible from some determinate distance. Therefore if the indivisible thing that is held to be sensible is seen from some determinate distance, like a divisible thing, then Aristotle’s argument will be conclusive. But if it is not possible to determine a distance from which it begins to be seen at the same time as a divisible thing is, it will again follow that in no way can it be seen. For one must take the proportion of the distance from which divisible things can be seen according to the proportion of the magnitudes that are seen. But there is no proportion of indivisible to divisible magnitude, for instance of a point to a line. Thus it will follow that what is indivisible cannot be seen from any distance, because any distance has a proportion to any other distance. Therefore it will follow that, if the indivisible thing is seen, it is seen by union with sight, which is contrary to the nature of sight and of the other senses that sense without touching. Therefore, an indivisible thing cannot be sensed—except, perhaps, inasmuch as it is the limit of a continuum, for other accidents of continua are also perceived in this way.

297. Then, when he says something has been said, then (449b1), he makes an epilogue to what was said in this book and establishes continuity with what follows. He says that something has been said about the sensitive parts—that is, the organs of sensing—and about sensible objects, and how they are related to the senses, both in general and with respect to each organ of sense, partly in this book, partly in the book On the Soul. Of what remains, the first to be considered are memory and recollection and sleep, because as present things are known by the sense power, so past things are known by memory, and there is a certain foreknowledge of future things in sleep.