Lecture 16 — Whether two senses can sense simultaneously

But there is also another such objection raised concerning the senses: whether it can happen that two sense simultaneously at the same indivisible point of time, or not?

If a greater movement always drives off a lesser, which is why people do not sense what is brought under their eyes if they are intensely thinking about something, or are afraid, or are hearing a loud sound. . . . Let this, then, be supposed, and also that one can sense anything better when it exists as simple than when mixed: for example, wine that is unmixed can be better sensed than wine that is mixed; and honey; and color; and a note alone better than one with the octave, because they obscure one another. Now it is things from which some one thing is made that do this.

If, then, a greater drives off a lesser, then, if they are simultaneous, even the former is, necessarily, less able to be sensed than if it were alone. For something is taken away by admixture of the lesser one, if indeed everything that is simple is better able to be sensed. Therefore, if they are equal, but exist as separate, neither will be sensible, for each obscures the other; and it is impossible to sense either as simple. Therefore either there will be no sensation, or there will be a different one out of the two. This seems to be brought about by things mixed together, whatever they may be mixed together into.

From some objects, something else can be made; but from some it cannot, and these are objects that come under different senses. For objects that can be mixed together have extremes that are contraries. But one object cannot be made out of white and high-pitched, except accidentally, but not in the way that a harmony is made out of high-pitched and low-pitched.

Therefore it is not possible to sense them simultaneously. For when their movements exist as equal, they will drive out one another, because one movement is not made out of them. But if they are unequal, it will be the stronger that causes sensation.

Moreover, it is more likely that the soul will simultaneously sense two objects of one sense, such as high-pitched and low-pitched, with the one sense: for it is more likely that movements of one sense would occur simultaneously than of two, for instance sight and hearing.

But it is not possible to sense two objects simultaneously with one, if they have not been mixed. For a mixture tends to be one thing. But one sense power at one moment has one object. And it is itself one at the one moment. Therefore it necessarily senses mixtures all at once, because it senses by means of one sense power in actuality.

For as numerically one in actuality, it has one object; but as specifically so, it is one in potentiality or power. Therefore, if it is one sense power in actuality, it will say that one object. Therefore, they are necessarily mixed together. Therefore, when they are not mixed, there will be two senses in actuality. But, with respect to one power, at one indivisible moment, there is necessarily only one operation, for there is only one use, and one movement, of one thing at one time, and it is one power. Therefore it is not possible to sense simultaneously two objects with one sense power.

But if this is impossible simultaneously in the case of objects that come under the same sense power if there are two of them, it is obvious that it is still less possible to sense simultaneously objects of two senses, such as white and sweet.

The soul seems to say that something is numerically one by nothing other than this “all at once”; but it seems to say that something is specifically one by the sense that judges, and by the manner.

What I mean is this. The same proper one will judge that, say, white and black are different. And one sense, different from that one, but itself the same, will judge that sweet and bitter are different. They judge each of the contraries in a different way, but they judge the corresponding elements in the same way: for instance, as taste judges sweet, sight judges white; and as the latter judges black, the former judges bitter.

253. But there is also another such objection (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; [254]).

Third, he determines the truth where he says with respect to the objection (448b17; [281]).

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 that while sight sees a color hearing simultaneously hears a voice.

254. Then, when he says if a greater movement (447a14), he argues for the false position, attempting to show that two senses cannot sense simultaneously.

First, he presents arguments to show this.

Second, he eliminates a false solution by which this position was maintained, where he says some of those who discuss symphoniae (448a19; [269]).

On the first point, he presents three arguments.

The first is based on alterations caused by sensible objects.

The second is based on the sense power itself; it starts where he says moreover, it is more likely (447b6; [258]).

The third is based on contrariety of sensible objects; it starts where he says moreover, if movements of contraries are contrary (448a1; [265]).

He prefaces the first argument with two presuppositions.

The first is that a greater movement drives back a lesser. Because of this, he says, the result is that often human beings do not sense what lies under their eyes, because of a more powerful movement. This may be an interior movement, whether of reason, as when they are intensely thinking about something, or of appetitive power, as when they are intensely afraid. Or it may be an external movement caused by some sensible object, as when they are hearing a loud sound. This, then, he says, is to be supposed as evidence.

255. The second presupposition is that anything is sensed better if it is simple than if it is mixed with something else, as wine has a stronger taste if it is pure than if it is mixed with water. The same is true of honey with respect to taste; and of color with respect to sight. And, with respect to hearing, it is true of one single note, which is better sensed if it is alone than if it is heard in harmony with another tone such as the octave, or in any other harmony. This is so because things mixed together obscure one another. But this second presupposition applies only to things from which one thing can be made, for such things alone are thoroughly mixed together.

256. From these two presuppositions he goes further when he adds if, then, a greater drives off a lesser (447a21). He says that if a greater movement drives back a lesser, as the first presupposition says, then, if both movements are simultaneous, even the greater one is necessarily less able to be sensed than if it were alone, because something of it is taken away by admixture of the lesser one, as appears from the second presupposition, namely that what is simple is better able to be sensed than what is mixed. It is significant that he has said if they are simultaneous, because the greater movement is sometimes so strong that it does not allow another movement to occur, and then it is not at all diminished by a lesser movement, because there is none. But if it does not prevail to the extent that it completely prevents the lesser movement from occurring, then, while the two movements exist, the lesser movement necessarily obscures the greater one to some extent. Therefore, if the movements are completely equal, but exist as different, neither will be sensible, because each wholly obscures the other—unless perhaps from the two movements one movement is made by mixture, but then what is simple in them cannot be sensed. And thus it must be either that no sensation of the equal movements occurs, or that there is a different sensation composed from both, that is, inasmuch as what is sensed is composed out of the two. And this is clearly the case in everything that is mixed together, because the mixture is not any of the things that are mixed together, but something else composed out of them. It is clear, then, from the foregoing that if two movements are unequal, the greater obscures the lesser, but if they are equal, either nothing or a mixture is sensed.

257. And from these points he proceeds further. He proposes that there are some objects (447a29) out of which some one thing can be made, but there are some out of which one thing cannot be made, and such are objects, such as color and odor, sensed by different senses. For only those objects can be mixed together in which the extremes are contraries, because mixture occurs by alteration. But objects that are sensed by different senses are not contrary to one another, and hence cannot be mixed together. For example, some one object is not made out of a white color and a high-pitched sound, except perhaps accidentally, inasmuch as they come together in the same subject; but not per se, in the way that a harmony is constituted out of a low-pitched and a high-pitched tone.

From this he concludes that it is in no way possible to sense (447b3) objects of different senses simultaneously, because if their movements are equal, they will entirely destroy one another, since one thing cannot be made out of them; but if they are unequal, the greater movement will prevail, and it alone will be sensed.

258. Then when he says moreover, it is more likely (447b6), he presents the second argument, which is based on the unity and plurality of the senses. He argues by denial of what is more likely.

It seems more likely that the soul is able to sense simultaneously two objects pertaining to one sense—such as high-pitched and low-pitched in sounds—by means of the one sense, than that it is able to sense simultaneously different objects pertaining to different senses by means of the two senses. He gives the following reason for this. To the extent that movements are more different, they seem less able to be attributed to the same thing. But two movements by which the soul, by means of different senses, senses different objects belonging to different genera are more different from one another than are two movements by which the soul perceives through one sense different objects belonging to the same genus. Hence it seems more likely that there could simultaneously be in one soul movements of one sense in relation to different sensible objects of the same genus, than movements of two senses, for instance sight and hearing.

259. Having presented this comparison, he eliminates what seems more likely. He says that it is not possible to sense simultaneously (447b9), by means of one sense, two objects, unless the two have been mixed together, and then when they have been mixed together, they are not two objects, because a mixture is naturally some one thing.

He proves in the following way that one sense cannot simultaneously know several things except to the extent that they become one thing by means of mixture. One sense power can be in actuality at one moment with respect to only one object, just as the terminus of any one operation or movement can be only something that is one. And a sense power in actuality must, at one and the same moment, be one and the same sense power in actuality; for no power simultaneously receives different forms. Thus if a sense power, for instance sight or hearing, has to sense several things simultaneously, it necessarily senses them inasmuch as they have been made one by mixture.

260. And this is because the sensitive power senses the two things by means of one sense power in actuality—that is, one sensitive operation. A sense power in actuality—that is, a sensitive operation— has numerical unity because it has one sensible object. But it is specifically one sense power in actuality—or one sensitive operation—because it is one in potentiality or power. For instance, all seeings of any visible things are specifically the same because of the unity of the power; but the seeing of one thing differs numerically from the seeing of another.

Therefore, if it is one sense power in actuality, it must “say”—that is, judge of—one object. Therefore, if there are many objects, they must be mixed together into one. Therefore, if they are not mixed, there must be two senses in actuality—that is, two sensitive operations.

261. But there is necessarily only one operation of one power at one and the same indivisible moment, because there can only be one use, and one movement, of one thing at one time. Hence, since sensitive operation is nothing but a “use” in which the soul uses a sensitive power, as well as a “movement” of the power itself, inasmuch as the sense is moved by a sensible thing, therefore, since one sense is one power, it is not possible to sense simultaneously two objects with one sense.

Therefore, if objects of one sense cannot be sensed simultaneously if there are two of them (447b21), it seems clear that it is still less possible to sense simultaneously objects of different senses, such as white and sweet.

262. Next he clarifies this inference. He says that the soul seems (447b24) to judge that something is numerically one in no other way than the thing’s being perceived by it all at once, for sensitive operation itself is numerically one inasmuch as it is all at once, as was said. But the soul says that something is specifically one not because the latter is sensed all at once, but because it is the same sense that judges of each of two objects, and because it is the same manner in which it senses each.

263. To explain what he said, he adds that the same proper one—that is, the same proper sense power—judges of two different objects, namely white and black. Likewise, a sense that itself is the same, judges sweet and bitter, for both are apprehended by the same sense, namely taste. But this sense that, while being the same, knows sweet and bitter, is different from the one that knows white and black. Nevertheless, one and the same sense knows each of the contraries in a different way: for it knows one as a possession and something perfect, and the other as a privation and something imperfect, since all contraries are related in this way. However, the way in which both senses know the corresponding elements—that is, the principles that analogously correspond to one another—is the same: for sight senses white the way taste senses sweet, and taste senses bitter as sight senses black.

264. Therefore it is clear that the soul judges that things are specifically different either by a different sense power, as in the case of white and sweet, or by a different manner of sensing, as in the case of white and black; but it judges that a thing is numerically one by perceiving it all at once. If, then, it is impossible for what is specifically one to be numerically one, it seems to be impossible for the soul to sense simultaneously either things that are known by different senses, or even things that are known by one sense but in different ways, and which seem to be less different from one another than are things known by different senses.