Lecture 25 — The common sense-objects and whether there is a sixth sense

That there is no other sense besides the five enumerated—I mean, sight, hearing, smell, taste, touch—anyone may believe from these things.

For if we have sensation of all the objects of the sense of touch (all varieties of the tangible being in fact sensible to us through touch), then, if we lack some sense, we must be lacking also in some sense organ.

Now, whatever we sense by contact is sensible to us through that sense of touch, which we do in fact possess. But whatever we sense through a medium and without contact is sensed through intervening simple things (I mean, for example, air and water); and in this case, things are so disposed that if several sense-objects, differing generically from one another, are perceptible through one thing, then, necessarily, what has a sense organ of this kind can perceive either object—e.g., if the organ is constituted of air, then air is the medium for both color and sound.

But if several work for the same thing (like both air and water for color, for both are transparent), then what has either of these will sense what is transmitted through each or by both.

Now, the sense organs are formed of these two simple bodies only, air and water. For the pupil is of water; the organ of hearing, of air; and smell, of either. But fire either is found in none or is common to all, for nothing without heat is sensitive. Earth either belongs to none or is especially involved in touch. Whence it remains that there is no sense organ without air and water. Now, certain animals do in fact possess these organs. All the senses, therefore, are found in animals neither incomplete nor defective (for even the mole is observed to have eyes beneath its skin). Therefore, if there is no other kind of body and no qualities other than those of the bodies here present, no sense will be missing.

But there cannot be a sense proper to the common things that we sense by each sense not accidentally: for example, movement, rest, shape, magnitude, number, and unity.

For we sense all these by motion: that is, we know magnitude by movement, and from magnitude, shape as well; for a shape is also a magnitude.

What is at rest is sensed as not moving, and number as the negation of the continuous and its properties. For each sense senses one thing. Whence it is manifest that it is impossible that there should be any proper sense for any of these.

The situation would, in that case, be as when we sense what is sweet by sight. This happens because the sensation of both is present in us, whereby when they coincide we are aware of it. If it were not so, we should sense this only accidentally, as when we see the son of Cleon not as the son of Cleon but as something white, which object happens to be the son of Cleon. But we already have a common sense of the common things, and this not merely accidentally. Hence, there is not a proper sense for them. If there were, we should never sense them except in the way we have said that we see the son of Cleon.

For the senses sense accidentally what is proper to each other, not in virtue of their very selves, but insofar as they are one when the sensation arises together in the same thing—as in the perception of bile as both red and bitter. For it does not pertain to either sense to say that these are one. Hence too one is deceived in thinking that if a thing is red, it is bile.

One might ask why we have several senses and not one only. Is it in order that the consequent and common things should be less hidden—for example, movement, magnitude, and number? For if there were no sense but sight alone, and that only of white as an object, these things would certainly be very hidden, and all things would appear alike because color and magnitude always accompany each other.

But the fact that the common things are attained by diverse sense powers makes it evident that each of them is a distinct object.

564. That there is no other sense (424b22). Here begins book 3 in the Greek text, (According to the Leonine edition, these words seem to have been added in a note to the text of Aristotle by William of Moerbeke.) for the good reason, apparently, that it is here that Aristotle begins to examine the intellect.

For there have been some who have asserted that sensation and intellect are the same thing. But clearly the intellect cannot be any one of the exterior senses already considered, (Lect. 14–24.) for its apprehension is not restricted to any one particular genus of sense-objects. So the remaining question is whether sensitivity includes any other cognitive power such as might lend support to the view that intellect is somehow one of the senses.

565. This section divides into three parts.

First, he asks whether there is any other sense besides the five exterior senses already treated.

Second, at now, if the soul is defined (427a17; [616]), he proves that the intellect is entirely distinct from the senses.

Third, at as to the part of the soul (429a10; [672]), he examines the intellectual part of the soul, having already clearly distinguished it from the senses.

The first of these sections has two parts:

first, he shows that there are no other proper senses besides the five exterior ones;

second, he shows that, besides these, there is a common sense, at since, however, we do sense that we see (425b12; [584]).

With regard to the first, he does two things:

first, he shows that there are only five particular senses;

second, he shows why there are several of them and not one only, at one might ask (425b4; [582]).

The former proof itself divides into two:

first, he shows that only the five senses apprehend their proper sensibles;

second, at but there cannot be (425a13; [575]), he shows that the same five are the only senses whose object is the common sensibles.

566. To prove the first of these two points, he argues thus. If someone has a sense organ in virtue of which he is naturally apt to know certain sensible objects, this organ knows all the sensible objects which are naturally suited by that organ. But the complete animals have all the organs of sense; therefore, they can know all sensible objects; and therefore, as these organs are only five in number, there will be no other sense than the five relative to the proper sensible objects.

567. In proposing this argument, Aristotle proceeds in this way: he first states his purpose in using it, that is, that from these things that follow, anybody may be sufficiently moved to believe that there are no other senses besides the five enumerated (424b22).

568. Second, at for if (424b24), he explains the major premise of the argument: that an animal possessed of any sense organ can know all that can be sensed by that organ. This he shows from the sense of touch, inasmuch as it is manifest how many tangible qualities exist; for it was said above that tangible qualities are the differences of the bodies made from elements as such, and these become manifest based on things that have been determined by the elements. (Lect. 23, nn. 546–48.) Whence it can be manifested to us that we ourselves sense all the tangible qualities.

569. He then applies the same principle—that we are aware of precisely such objects as correspond to a given sense organ in us—to the other senses. So he says: if we have sensation of all the objects of the sense of touch (which is apparent from the fact that all the tangible passions are sensed by us), then it must be said universally that, if we lack some sensation of a sensible quality, the reason must be that we lack the sense organ that is naturally apt to know that sensible, precisely because if we should have the sense organ, we would know the sensible qualities. And this, because it is being said universally, he then supports with particular examples.

570. And first, with respect to things we apprehend without any extrinsic medium; for he says that whatever we sense by contact, that is, without an extrinsic medium, is reached by the organ of touch (which we have). But where, as in the other senses, certain extrinsic media that are simple bodies, like air and water, come between us and the object, and without touching it, if several sense-objects, differing generically from one another, are perceptible through one organ, then, necessarily, that which has an organ of this kind senses each genus of object;

For example, if a sense organ is constituted of air, and air can be modified by both color and sound, then what has such an organ will be able to perceive both color and sound. If, on the contrary, several different organs are receptive of the same sensible object—as happens in the case of organs composed, the one of air, the other of water, which are both transparent and therefore both receptive of color—then an animal with either of such organs is able to perceive whatever is perceptible through each, as through media, or by both, as by instruments. The reason for his saying this is that the senses that sense through an extrinsic medium share the form of their media; and he adds these conditions because the same sensible object, for instance, odor, is sensed both by one animal through water and by another through air.

571. Third, at now, the sense organs are formed (425a3), he makes and explains a further statement: that the complete animals possess all the organs of sense. These organs, he says, are by nature composed of only two of the simple bodies, namely air and water, these being the two most passive simple bodies, and the condition of the sense organ requires this so that it may be easily modified by the sense-object. For the pupil of the eye contains water, since through the aqueous humor within the eye, the eye receives the species of the visible object; likewise, the organ of hearing contains air (as we have noted already); (Lect. 17, n. 453.) the sense of smell is related by some to air and by some to water. (Lect. 20.) Fire, on the other hand, by reason of its extreme activity and minimal passivity, in itself is found in none of the sense organs, though in virtue of a participation in its own quality it is common to all the senses; for nothing without heat is sensitive, because nothing senses without life.

572. Earth either belongs to none of the sense organs, or, through its entering into composition, it is especially appropriated to touch; for the organ of touch must be of an intermediate composition, as was said above, and consequently it must be composed of all the elements. (Lect. 23, nn. 546–48.)

Whence it remains that there is no organ of sense beside those of air and water; and certain animals, that is, the complete animals, have these organs of air and water. So he concludes by saying that all the senses are found in animals that are not incomplete according to their own nature, such as the incomplete immobile animals that have only the sense of touch.

573. These stand apart, too, from the defective, that is, defective animals, lacking a sense due to some non-natural cause, like blind or deaf men. But the mole, for example, which belongs to the genus of complete animals, is observed to have eyes beneath its skin; thereby it is like its own genus. But due to its living underground, it does not need sight; and if its eyes were uncovered, the soil would aggravate them.

574. Clearly this argument assumes a determinate number of elements. From this it follows that the sense organs that reach their objects through an exterior medium must be composed exclusively of air and water. Again, it presumes a fixed number of elemental qualities, which are the tangible qualities; whence, through them it becomes known that we know all the tangible qualities.

Therefore he concludes that we are missing no sense—unless someone wants to say that there is some elementary body besides the four elements, and that there are other passions that can be discerned by touch that do not belong to the bodies around us and known to us. And that seems incongruous. Whence what is left is that there are only the five senses that we have.

575. Then, where he says, but there cannot be (425a13), he rejects the suggestion that the common sensibles are the object of another and distinct sense. For the proper sense-object of any one sense is only known accidentally by any other sense; but the common sensibles are not sensed accidentally by any sense at all; rather, they are each known through themselves by several senses. Therefore they cannot be the proper objects of any one sense.

576. Note how this argument proceeds.

Aristotle first states the conclusion, that there cannot be a proper sense organ adapted to know of the common sense-objects, which we sense by means of each sense through themselves, not accidentally, namely, movement, rest and so forth.

577. Then, at for we sense (425a16), he shows that these common sensibles are sensed through themselves, and not accidentally. For what is sensed precisely by modifying the sense is sensed through itself, not accidentally; for to sense in itself is simply to undergo something from the sensible object. Now, all these common sensibles are known through a certain modification, which is why he says that we sense all these by motion, that is, by a certain modification. For magnitude obviously modifies the sense, since it is the subject of a sensible quality, like color or flavor, and no quality is able to act in separation from its subject. From which it is apparent that shape also is known through a certain modification, for shape belongs to magnitude, since it consists in the boundary of magnitude. As Euclid says, shape is what is contained in a limit. (Euclid, Elements, bk. 1, def. 14.)

578. Rest also is perceived by means of movement, as darkness by means of light, for rest is the privation of motion. And number is known through negation of the continuous, which is a magnitude (for the number of sensible things is caused by the division of the continuous); whence also the properties of number are known through the properties of the continuous (for as the continuous is infinitely divisible, numbers can also grow to infinity, as is shown in Physics 3). (Aristotle, Physics 3.7, 207b10–15; cf. Aquinas, Commentary on Physics, bk. 3, lect. 7–10.) It is also clear that through itself each sense knows one thing, so that it might be modified by one object; whence it is clear that these common sensibles are sensed through themselves, and not accidentally. From that he concludes that it is impossible that there should be any proper sense for any of these.

579. Then, at the situation (425a21), he shows that if they were the object of any proper sense, they would be accidentally sensed. This is why he says that in that case, if the common sensibles were the proper objects of some sense, this would be as when we sense what is sweet by sight. For this happens because we have a sense for both of these (the sweet and the white); hence, when both are found in one thing, that which belongs to one sense is known accidentally by the other.

580. But if an object is not sensible to a certain sense, it can never be sensed accidentally due to a coincidence of two senses in the same thing, but it must always, in every respect, be accidentally sensible, as was said. (Lect. 13, n. 395.) Thus we sense accidentally the son of Cleon not as the son of Cleon but as white, to which it is accidental that it is the son of Cleon. But being the son of Cleon is not (like sweetness) accidentally visible in such a way that it is sensible through itself to some other sense. On the other hand, we have a common sense of the common sensibles*, and this not merely accidentally*, that is, the common sensible objects are sensed commonly by the diverse senses through themselves, and not accidentally. It follows that there is not a proper sense for them; if there were, we would not sense them except accidentally, the way we sense Cleon’s son accidentally.

581. The senses sense the proper sensible objects accidentally, as sight that of hearing, and vice versa. For sight does not know the audible, nor hearing the visible in virtue of their very selves (for the eye undergoes nothing from the audible, nor the ear from the visible), but both insofar as they become one sense, that is, one actual sensation, so that we may say thus, in the same sensible object. I call them the same sense in act due to the fact that the action of each sense occurs together in relation to the same sensible thing, as when bile is at once seen as red and tasted as bitter; so that as soon as we see that something is red we judge that it is bitter. But there is not some other sense to which it is proper to know that the red (The Latin text has “white” (album) here; presumably, this is an oversight.) and the bitter are one, for this unity is quite accidental, and what is accidental cannot be the object of any special power. And because sight only accidentally perceives a flavor, the sense is often deceived, and we judge that because a certain thing is red, it is therefore bile.

582. Then, at one might ask (425b4), he goes on to inquire why there are many senses. As this is a question about a species as a whole, it must be answered in terms of final causality (as he explains towards the end of On the Generation of Animals), not, like questions about individual peculiarities, in terms of material or efficient causality. (Aristotle, On the Generation of Animals 5.1, 778a29–b1.) So here he introduces the idea of final cause.

The question might arise, he says, why we have several senses, and not only one; and he answers that it is so that such things as movement, magnitude, and number should not be hidden from us; these are things that follow on the proper sensible objects and are common to the diverse sense-objects. For if there were no sense but sight alone, whose proper object is only color, and color and magnitude follow on each other since along with the color the sense is modified by magnitude, we should never be able to distinguish between color and magnitude; they would appear alike. But the fact that magnitude is also sensed by a sense other than sight, while color is not, is enough to show us that magnitude and color are distinct. And the same holds good for the other common sensibles.

583. To this one might add also the following argument for the distinction of the senses. Since every potency is spoken of in reference to its object, there must be a diversity of sensitive potencies according to the difference of the objects. But objects are sensible insofar as they can modify a sense; hence, to the different genera of such modifications of the senses due to the sensibles there must correspond a diversity of senses.

Now, one way in which the sense is modified by a sense-object is by contact, whence arise both the sense of touch, which discerns things that compose an animal, and the sense of taste, which is perceptive of qualities that indicate the suitability of nourishment for preserving an animal.

And another way a sense is modified is through an extraneous medium; and this modification involves either an alteration of the sensible object, as when an odor modifies the sense along with a disintegration of the thing smelled; or along with a certain local motion, as sound modifies it; or without any modification of the sensible object, but simply through a spiritual modification of the medium and the organ, such as is made by color.