Thomas Aquinas

“ Although sense and appetite are principles of movement in perfect animals, yet sense and appetite, as such, are not sufficient to cause movement, unless another power be added to them; for immovable animals have sense and appetite, and yet they have not the power of motion. Now this motive power is not only in the appetite and sense as commanding the movement, but also in the parts of the body, to make them obey the appetite of the soul which moves them. ”

“ And there is yet another genus in the powers of the soul, which genus regards a still more universal object---namely, not only the sensible body, but all being in universal. Wherefore it is evident that the latter two genera of the soul's powers have an operation in regard not merely to that which is united to them, but also to something extrinsic. Now, since whatever operates must in some way be united to the object about which it operates, it follows of necessity that this something extrinsic, which is the object of the soul's operation, must be related to the soul in a twofold manner. ”

“ For the powers are not for the organs, but the organs for the powers; wherefore there are not various powers for the reason that there are various organs; on the contrary, for this has nature provided a variety of organs, that they might be adapted to various powers. In the same way nature provided various mediums for the various senses, according to the convenience of the acts of the powers. And to be cognizant of the natures of sensible qualities does not pertain to the senses, but to the intellect. ”

“ Avicenna, however, assigns between the estimative and the imaginative, a fifth power, which combines and divides imaginary forms: as when from the imaginary form of gold, and imaginary form of a mountain, we compose the one form of a golden mountain, which we have never seen. ”

“ As the Philosopher seems to say (De Anima ii, 11) , the sense of touch is generically one, but is divided into several specific senses, and for this reason it extends to various contrarieties; which senses, however, are not separate from one another in their organ, but are spread throughout the whole body, so that their distinction is not evident. But taste, which perceives the sweet and the bitter, accompanies touch in the tongue, but not in the whole body; so it is easily distinguished from touch. ”

“ The "natural appetite" is that inclination which each thing has, of its own nature, for something; wherefore by its natural appetite each power desires something suitable to itself. But the "animal appetite" results from the form apprehended; this sort of appetite requires a special power of the soul---mere apprehension does not suffice. ”

“ For a thing is desired as it exists in its own nature, whereas in the apprehensive power it exists not according to its own nature, but according to its likeness. Whence it is clear that sight desires naturally a visible object for the purpose of its act only---namely, for the purpose of seeing; but the animal by the appetitive power desires the thing seen, not merely for the purpose of seeing it, but also for other purposes. But if the soul did not require things perceived by the senses, except on account of the actions of the senses, that is, for the purpose of sensing them ”

“ The nutritive and the augmentative have their effect where they exist, since the body itself united to the soul grows and is preserved by the augmentative and nutritive powers which exist in one and the same soul. But the generative power has its effect, not in one and the same body but in another; for a thing cannot generate itself. Therefore the generative power, in a way, approaches to the dignity of the sensitive soul, which has an operation extending to extrinsic things, although in a more excellent and more universal manner ”

“ Since, therefore, magnitude and shape are further from color than sound is, it seems that there is much more need for another sensitive power than can grasp magnitude or shape than for that which grasps color or sound. ”

“ Movement and rest are sensed according as the subject is affected in one or more ways in the magnitude of the subject or of its local distance, as in the movement of growth or of locomotion, or again, according as it is affected in some sensible qualities, as in the movement of alteration; and thus to sense movement and rest is, in a way, to sense one thing and many. Now quantity is the proximate subject of the qualities that cause alteration, as surface is of color. Therefore the common sensibles do not move the senses first and of their own nature, but by reason of the sensible quality ”

“ Wherefore, since the sensitive power is the act of a corporeal organ, it follows that the power which receives the species of sensible things must be distinct from the power which preserves them.
Again we must observe that if an animal were moved by pleasing and disagreeable things only as affecting the sense, there would be no need to suppose that an animal has a power besides the apprehension of those forms which the senses perceive, and in which the animal takes pleasure, or from which it shrinks with horror. ”

“ Now we must observe that for the life of a perfect animal, the animal should apprehend a thing not only at the actual time of sensation, but also when it is absent. Otherwise, since animal motion and action follow apprehension, an animal would not be moved to seek something absent: the contrary of which we may observe specially in perfect animals, which are moved by progression, for they are moved towards something apprehended and absent. ”

“ The modes of living are distinguished according to the degrees of living things. There are some living things in which there exists only vegetative power, as the plants. There are others in which with the vegetative there exists also the sensitive, but not the locomotive power ”

“ Therefore the power by which in other animals is called the natural estimative, in man is called the "cogitative," which by some sort of collation discovers these intentions. Wherefore it is also called the "particular reason," to which medical men assign a certain particular organ, namely, the middle part of the head: for it compares individual intentions, just as the intellectual reason compares universal intentions. As to the memorative power, man has not only memory, as other animals have in the sudden recollection of the past ”

“ Generation of inanimate things is entirely from an extrinsic source; whereas the generation of living things is in a higher way, through something in the living thing itself, which is the semen containing the principle productive of the body. ”

“ Now, we must observe that as to sensible forms there is no difference between man and other animals; for they are similarly immuted by the extrinsic sensible. But there is a difference as to the above intentions: for other animals perceive these intentions only by some natural instinct, while man perceives them by means of coalition of ideas. ”

“ But for the retention and preservation of these forms, the "phantasy" or "imagination" is appointed; which are the same, for phantasy or imagination is as it were a storehouse of forms received through the senses. Furthermore, for the apprehension of intentions which are not received through the senses, the "estimative" power is appointed: and for the preservation thereof, the "memorative" power, which is a storehouse of such-like intentions. ”

“ Yet they are not accidental sensibles, for they produce a certain variety in the immutation of the senses. For sense is immuted differently by a large and by a small surface: since whiteness itself is said to be great or small, and therefore it is divided according to its proper subject. ”

“ There are others which besides this have locomotive powers, as perfect animals, which require many things for their life, and consequently movement to seek necessaries of life from a distance. And there are some living things which with these have intellectual power---namely, men. But the appetitive power does not constitute a degree of living things ”