Lecture 24 — General conclusions on sensation

It must be taken universally that all sensation is the receiving of species without matter, just as wax receives the sign of the signet-ring without the iron or gold. It receives the mark of the gold or bronze, but not insofar as it is gold or bronze. Similarly, the sense of any sense-object is acted upon by a thing having color or flavor or sound, not, however, in respect of what each is called as a particular thing, but insofar as each is of a certain sort and according to its account.

The primary sensitive part is that in which a power of this sort resides. They are therefore indeed the same thing, but they differ in mode of being. For what is acted upon in sensation will be a magnitude, but neither being sensitive nor sensation is a magnitude. Each is, rather, a certain ratio and a power of that magnitude.

It is clear from these facts why the excess of sensible qualities destroys the sensitive power. For if the motion is too strong for the sense, the ratio—which is the sense—is lost. It is as with tone and harmony when the strings are violently struck. Also, on account of this it is plain why plants do not sense, though they have some share in soul and are acted upon by tangible objects to become hot or cold. The reason is that they lack the mediate state, nor do they have a principle of the sort that is able to receive the species of sense-objects, but they are acted upon with matter.

It might be asked, is anything acted upon by odor, if it cannot have the sense of smell—or by color, if it is unable to see? And so in the other cases.

But if what can be smelled is odor, whatever causes smell is odor. Hence things incapable of smelling cannot be acted upon by odor. The same argument holds for the other senses. And of subjects that can perceive, the ability belongs to them only in virtue of each being sensitive.

The same is evident thus: neither light or darkness or sound or odor affect bodies, but only what they occur in does so; e.g., it is the air which accompanies thunder that smashes trees.

But things tangible and savors do so affect things. If not, what is it that non-souled things are affected and changed by? Therefore, do not also the other sense-objects have a like effect?

But not every body is acted upon by odor or sound, such recipients being only things indeterminate and unstable, like air, which may stink, as though acted upon somehow.

What, then, is it to smell, save to be acted upon somehow? But to smell is to sense. Air, however, being so acted upon, becomes rapidly sensible.

551. It must be taken universally (424a17). Having examined each of the senses separately, the Philosopher now draws a conclusion about sensation. About this he does three things.

First, he explains what sensation is.

Second, at it is clear (424a28; [556]), he solves certain problems connected with that definition of sensation.

And third, at it might be asked (424b3; [558]), he raises certain questions about the way a sense is affected by its object.

As regards the first point, he does two things.

First, he shows what sensation is;

second, he shows what the organ of sensation is, at the primary sensitive part (424a24; [555]).

First, then, he says that it must be taken universally, and as commonly present in every sensation, that all sensation is the receiving of species without matter, just as wax receives the sign of the signet-ring without the iron or gold.

This, however, would seem to be common to all cases of being acted upon; for every patient receives from an agent insofar as the agent is acting; and since the agent acts through its form, not its matter, every patient receives the form without matter. And this indeed is sensibly apparent; for example, air does not receive matter from fire acting upon it, but form. So it would seem not to be peculiar to sensation that it receives species without matter.

552. I answer that, while it is true that every patient receives form from an agent, there are differences in the manner of receiving. For form received in a patient from an agent sometimes has the same mode of existence in the patient as it has in the agent; and this occurs when the patient has the same disposition to the form as the agent has. For whatever is received is received according to the manner of the receiver; so that, if the patient is disposed as the agent is, the form is received in the patient in the manner in which it exists in the agent. And then the form is not received without matter; for although it and numerically the same matter that is in the agent does not come to belong to the patient, nevertheless, the patient becomes, in a way, the same, inasmuch as it acquires the same material disposition to the form that was in the agent. And it is in this way that air is acted upon by fire, and in the same way is whatever else is acted upon with a natural passion.

553. Sometimes, however, the form is received in the patient according to a manner of existence other than was in the agent, because the material disposition of the patient to receive form is not like the material disposition that was in the agent. In these cases, then, the form is received in the patient without matter, inasmuch as the patient is made like the agent according to form and not according to matter. And it is thus that a sense receives form without matter, the form having, in the sense, a different manner of being than that which it has in the sensible reality. For in the sensible reality it has a natural existence, but in the sense it has an intentional or spiritual existence.

554. Aristotle finds an apt example of this in the signet-ring and wax. For the disposition of the wax to the image is not the same as that of the iron or gold.

Hence, wax, he says, receives the sign (424a20), that is, a shape or image of what is gold or bronze, but not insofar as it is gold or bronze. For the wax becomes like the gold signet-ring in respect of its image, but not in respect of the disposition of gold. Similarly, the sense is acted upon by the sense-object by a thing having color or flavor (that is, taste) or sound, not, however, in respect of what each is called as a particular thing, that is, it is not acted upon by a colored stone precisely as stone, or by sweet honey precisely as honey, because in the sense there arises no similar disposition to the form that was present in those subjects; but it is acted upon by them insofar as each is of a certain sort, that is, insofar as it is colored or tasteable, and according to its account, that is, according to form. For the sense is assimilated to the sensible object according to form, not according to the disposition of matter.

555. Next, at the primary sensitive part (424a24), he concludes about the organ of sense. Since from his teaching that sense receives species without matter—which is true of the intellect also—one might be led to suppose that sense was not a power in a body, like the intellect, to preclude this error, Aristotle assigns to sense an organ, observing that the primary sensitive part, that is, the first organ of sense, is that in which a power of this sort resides, namely a capacity to receive species without matter. For a sense organ, for example, the eye, shares the same subject with the power itself, but they differ in mode of being, because the power differs from the body in its account, for the power is, as it were, the form of the organ, as was said above. (Lect. 8, nn. 230–31.) So he goes on to say a magnitude, that is, a bodily organ, is what is acted upon in sensation, that is, is the receptive subject of the sense power, as matter of form; but the magnitude and the sensitivity or sense differ by account, the sense being a certain ratio, that is, proportion and form, and a power of that magnitude.

556. Then, when he says, it is clear (424a28), he infers from these premises a reply to two questions that might arise.

From what has been said, he observes, it is clear why an excess in the object destroys the organs of sense; for, if sensation is to take place there must preexist in the organs of sense a certain ratio, that is, a proportion, as was said. But if the motion of the sense-object is stronger than what the organ is naturally able to bear, the proportion is lost and the sense itself, which consists, as has been said, in a certain proportion of the organ, is corrupted. It is as though one were to twang cords violently, destroying the tone and harmony of the instrument, which consists in a certain proportion.

557. His analysis also gives us the answer to another question, namely, why plants do not sense, though they have some share in soul and are acted upon by certain sensible objects, that is, tangible things (for it is manifest that they heat up and cool down). The reason why they do not feel is that they lack the proportion needed for sensation; in particular, they do not have that mediate state in complexion between the tangible qualities, which is a prerequisite of the organ of touch, apart from which there can be no sensation. Hence, they have no intrinsic principle of the sort that can receive a species without matter, that is to say, no sense. But they are acted upon with matter, that is, according to a material change.

558. Next, when he says, it might be asked (424b3), he raises a question about the sense-object’s action on the senses, because he said that plants are acted upon by tangibles. He raises the question whether a subject can ever be acted upon by objects other than those of which it possesses the sense, for example, by odor if it cannot have the sense of smell, or by color, if it has no sight, or by sound, if it is without hearing.

559. Then, at but if what can be smelled is odor (424b5), he brings two reasons against this suggestion.

In the first place, it is proper to what can be smelled to cause smell, whereas odor is such, so if anything causes smell, it causes it by odor. Whence it follows that whatever lacks a sense of smell cannot be acted upon by odor. And the same argument holds for the other senses, that it is impossible that anything whatever might be acted upon by sense-objects; this can only happen in things endowed with sense.

560. At the same is evident thus (424b9), he states the second reason, as follows. The above argument is confirmed by experience. For light and darkness, smell and sound, produce no effect on bodies without sensation, except accidentally, inasmuch as the bodies with those qualities do something, like the air that smashes trees when it thunders; therefore the tree is acted upon not by the sound, properly speaking, but rather by the moving air.

561. Then, at but things tangible and savors (424b12), he shows that it is otherwise with tangible qualities; tangible things and savors, that is, flavors, do so have an effect on things without sensation. (But this is to be understood of the flavors not as such, but just insofar as the tasteable is something tangible, and taste a sort of touch.) For if insensitive things were not acted upon by tangible qualities, there would be no question of non-souled things being acted upon and altered at all, these tangibles being the active and passive qualities of the elements in virtue of which all bodily alterations take place.

562. Next, at but not every body (424b14), he shows that other sense-objects act on non-souled things, though not on all. For, in asking, therefore, do not other sense-objects have a like effect on non-souled things as odor does? he implies that they do. Yet not every body is acted upon by odor and sound, though all are by heat and cold. But such sense-objects are acted upon only by unstable, indeterminate bodies*, like air* and water, which, being fluid, are not very self-contained; and that air can be acted upon by odor is obvious enough since it can stink. Another reading for “stink” (fetet) says “bears” (feret), meaning that the species is borne to the other senses by the medium for the sake of sensation. The reason for this difference is that, as tangible qualities are causes of the other sense-objects, they have more of an active power and can act on all bodies whatsoever, whereas the other sense-objects, having less of an active power, can act only on things that are especially impressionable. The same account applies to the luminosity of the heavenly bodies, which alter lower bodies.

563. Lastly, at what, then, is it to smell (424b16), he solves the problem raised by the argument stated above. If a thing, he asks, can be acted upon by odor and yet not smell it, what is it to smell other than to be acted upon by the smell? And he answers that smelling happens when a thing is acted upon by odor in such a way as to sense it. But air is not acted upon in this way, nor does it sense it, since it has no sensitive potency; rather, it is acted upon only so as to become a sense-object, inasmuch as it is a medium for sensation.