Article 13 — The distinction between the powers of the soul

Thirteenth, it is asked about the distinction between the powers of the soul, that is, whether the powers of the soul are distinguished from one another by their objects. (Parallel texts: ST I.77.3; In I Sent., d. 17, q. 1, a. 4; II Sent., d. 44, q. 2, a. 1; Commentary on Aristotle’s On the Soul, bk. 2, lect. 6. For a detailed treatment of the various powers of man, see ST I.78–82.)

Obj. 1: It seems that they are not. For the things which differ most from one another are contraries. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 21.) But a contrariety of objects does not diversify powers, because the same power of vision apprehends both white and black. Therefore, a difference of objects does not diversify powers. (Cf. ST I.77.3, obj. 2.)

Obj. 2: Further, things which differ substantially differ more than those which differ accidentally. Now a man and a stone differ substantially, whereas a sound and something colored differ accidentally. Therefore, since a man and a stone are apprehended by the same power, so much the more so are a sound and something colored. Hence, a diversity of objects is not the cause of the diversity of powers.

Obj. 3: Further, if a difference of objects were the cause of the diversity of powers, one and the same object would necessarily cause powers to be identical. Now we see that one and the same object is apprehended by different powers. For the same object is known and desired because an intelligible good is the object of the will. Consequently, a diversity of objects is not the cause of the diversity of powers. (Cf. ST I.77.3, obj. 3.)

Obj. 4: Further, wherever the cause is the same, the effect is also the same. Therefore, if different objects diversified some powers, they would necessarily have to cause a diversity of powers in every case. However, we do not observe this. For sometimes different objects are certainly related to different powers, as sound and color are related to hearing and to vision respectively; and, at other times, these same objects are related to one and the same power, namely, to the imagination and to the intellect. Hence, it follows that a diversity of objects is not the cause of the diversity of powers. (Cf. ST I.77.3, obj. 4.)

Obj. 5: Further, habits are perfections of powers. Moreover, perfectible things are distinguished from one another by their proper perfections. Consequently, powers are distinguished by their habits and not by their objects. (Cf. Aquinas, On Truth, q. 15, a. 2, obj. 11; Commentary on the Nicomachean Ethics, bk. 2, lect. 5, n. 298.)

Obj. 6: Further, whatever exists in a thing exists in it according to the mode of the recipient. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 12.) But the powers of the soul exist in the organs of the body, for they are the acts of these organs. Therefore, the powers of the soul are distinguished by the organs of the body and not by their objects. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 4; In I Sent., d. 3, q. 4, a. 2, s.c. 3; On Truth, q. 15, a. 2; SCG II.82; Averroes, Commentary on Aristotle’s On the Soul, bk. 1, comm. 7.)

Obj. 7: Further, the powers of the soul are not the essence itself of the soul but are properties of it. Now the properties of a thing spring from its essence. However, only one thing comes directly from a single thing. (Cf. ST I.77.6, obj. 1.) Therefore, first of all one single power of the soul comes from its essence, and then the other powers proceed therefrom in a certain order through the medium of this power. Hence, the powers of the soul differ according to origin and not according to objects.

Obj. 8: Further, if the powers of the soul are diverse, one of them must come from another, for all of them do not come directly from the essence of the soul, because it is one and simple. But it is seen to be impossible for one power of the soul to come from another. First, because all powers of the soul exist simultaneously. Second, because accidents have their existence in a subject, and one accident cannot be the subject of another. Therefore, the diversity among the soul’s powers cannot be a result of the diversity among objects.

Obj. 9: Further, the higher a substance is, the greater is its power and, as a result, less diversified, because every simple power is unlimited more than it is multiplied, as is said in The Book of Causes. (The Book of Causes, proposition 17 [18]; Aquinas, Commentary on the Book of Causes, proposition 17.) Now the soul is the most perfect of all inferior beings. Therefore, its power is more unified than theirs and still extends to many things. Consequently, its power is not multiplied because of the diversity among objects.

Obj. 10: Further, if the diversity among the soul’s powers depends on the diversity among objects, the order among the soul’s powers must also depend on the order among these objects. However, this is seen not to be the case, for the intellect, whose object is the quiddity and substance, is subsequent to the senses, whose objects are accidents such as color and sound. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 10.) Furthermore, touch is prior to sight, while the visible is prior to and more common than the tangible. Consequently, there is not a diversity of powers merely because there is a difference of objects.

Obj. 11: Further, every appetible object is either sensible or intelligible. (Cf. Aristotle, On the Soul 3.10, 433b10–12.) Now the intelligible is the perfection of the intellect, and the sensible is the perfection of sense. Therefore, since any being naturally desires its perfection, it follows that intellect and sense naturally desire every appetible object. Hence, it is unnecessary to admit the existence of any appetitive power other than the sensitive.

Obj. 12: Further, no appetite exists except the will and the irascible and concupiscible appetites. But the will belongs to the intellective order, and the concupiscible and irascible appetites belong to the order of sense, as is pointed out in On the Soul 3. (Aristotle, On the Soul 3.9, 432b5–7; cf. Aquinas, Commentary Aristotle’s On the Soul, bk. 3, lect. 8.) Therefore, no appetitive power must be held to exist in addition to the sensitive and intellective.

Obj. 13: Further, the Philosopher proves in On the Soul 3, that the principles of local motion in an animal are sense or imagination, intellect and appetite. (Aristotle, On the Soul 3.10, 433a9–13.) But a power in animals is nothing else than a principle of movement. Therefore, there is no motive power except the cognitive and appetitive powers.

Obj. 14: Further, the powers of the soul are directed to something higher than nature, otherwise there would be powers of the soul in all natural things. But the powers which are assigned to the vegetative soul do not appear to be directed to anything higher than nature. For the vegetative soul is directed to the conservation of the species through generation, to the preservation of the individual through nutrition, and to the development of the individual’s proper size through augmentation. Now in natural things, nature, too, performs all of these activities. Consequently, the powers of the soul must not be directed to such activities.

Obj. 15: Further, the higher a power, the greater is its unity and the more numerous are the things to which it extends. But a power of the soul is higher than a power of nature. Therefore, since nature by one and the same power gives existence to a natural body, bestows on it its proper size, and preserves it in existence, it seems a fortiori that the soul does these things through one power. Therefore, the generative, nutritive, and augmentative powers are not diverse powers.

Obj. 16: Further, sense is cognizant of accidents. But certain other accidents differ from one another to a greater degree than do sound and color and the like, which exist not only in the same genus of quality, but also in the same species, namely, the third kind of quality. (Cf. Aristotle, Categories 8, 9a28–10a10; Aquinas, Commentary on Aristotle’s Metaphysics, bk. 5, lect. 16; Commentary on Aristotle’s On the Soul, bk. 2, lect. 14.) Therefore, if powers are distinguished according to the difference of objects, the powers of the soul should not be distinguished by accidents of this kind, but rather by others which differ from each other to a greater degree.

Obj. 17: Further, there is one first contrary in any genus. (Cf. Aristotle, Metaphysics 10.4, 1055a23–33; On the Soul 2.11, 422b23–27; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 22; Averroes, Commentary on Aristotle’s On the Soul, bk. 2, comm. 107.) Therefore, if the sensitive powers are diversified because of the different genera of possible qualities, it seems that there are diverse sensitive powers wherever there are diverse contraries. Now in some cases this does occur, for sight apprehends both white and black, and hearing apprehends both low and high notes; but in other cases it does not, for touch apprehends both hot and cold, wet and dry, soft and hard, and so on. Consequently, powers are not distinguished from one another by their objects.

Obj. 18: Further, memory does not appear to be a power distinct from sense. For, according to the Philosopher, memory is a passion of a first sense. (Aristotle, On Memory and Recollection 2.1, 450a14.) However, their objects differ because the object of sense exists in the present, and the object of memory in the past. Hence, powers are not distinguished from one another by their objects.

Obj. 19: Further, all things known by the senses are also known by the intellect, which is cognizant of many other things as well. Therefore, if the sensitive powers are distinguished from one another by reason of a plurality of objects, the intellect must also be distinguished into different powers, just as sense is. This is evidently false.

Obj. 20: Further, the possible and agent intellect are different powers, as has been shown above. (Above: qq. 3–5.) But the object of both is the same. Therefore, powers are not distinguished from one another because of a difference of objects. (Cf. Aquinas, On Truth, q. 15, a. 2, obj. 13.)

On the contrary (1), it is said in On the Soul 2 that powers are distinguished by acts, and acts by objects. (Aristotle, On the Soul 2.4, 415a14–22; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 6.)

Furthermore (2), perfectible things are distinguished from one another by their perfections. But the objects of powers are the perfections of powers. Therefore, powers are distinguished by their objects.

I answer that a power as such is spoken of in relation to an act. Hence, a power must be defined by its act, (Cf. Aristotle, Metaphysics 9.8, 1050a7; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 5; On Truth, q. 15, a. 2, resp., ad 12.) and powers in turn are distinguished from one another inasmuch as their acts are different. Now acts derive their species from their objects, (Cf. Aristotle, Physics 5.1, 224b7; Aquinas, In II Sent., d. 38, q. 1, a. 4, obj. 1; On Truth, q. 15, a. 2, resp.; Commentary on Aristotle’s On Sense and What Is Sensed, tract. 1, ch. 18.) because, if they are acts of passive powers, their objects are active. (Cf. Aristotle, On the Soul 2.4, 415a16–22; Averroes, Commentary on Aristotle’s On the Soul, bk. 2, comm. 33; Aquinas, Commentary on Aristotle’s On the Soul, bk. 1, lect. 8; bk. 2, lect. 25; bk. 3, lect. 8; Commentary on Aristotle’s On Sense and What Is Sensed, tract. 1, ch. 10; On Truth, q. 2, a. 2, ad 2; q. 15, a. 2, resp.) However, if they are the acts of active powers, their objects are as ends. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 6; On Truth, q. 16, a. 1, ad 13.) Now the species of an operation must be considered in both of these ways. For the act of heating and that of making cold are distinguished from one another, because the principle of the former is heat, and that of the latter, cold. Besides, both are terminated in similar ends. For an agent acts in order that it may cause something similar to itself to exist in another. (Cf. Aquinas, In IV Sent., d. 19, q. 1, a. 2, ad 1; Commentary on Aristotle’s On the Soul, bk. 2, lect. 9 and 30.) It follows, therefore, that the distinction between the powers of the soul is based on a difference of objects. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 13, n. 387; On Truth, q. 15, a. 2, resp.)

Now it is necessary to consider the difference among objects inasmuch as they are objects of the soul’s activities, and not according to some other way. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 6.) For a species is differentiated in any genus only by the specific differences which essentially divide the genus. The species of “animal,” for instance, are not distinguished by white and by black, but by rational and non-rational.

Furthermore, it is necessary to consider three grades in the actions of a soul. For the action of a soul transcends that of the nature operating in inanimate things. But this occurs in two ways. First, with respect to the manner of acting; second, with respect to what is produced by the action. (Cf. Aquinas, On Truth, q. 10, a. 1, ad 2.) Now with respect to the manner of acting, every action of a soul must transcend the operation or action of an inanimate nature. For every operation of a soul must proceed from some intrinsic agent, because an action of a soul is a vital action, and moreover, every living thing is one that moves itself to operation. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 5.) However, so far as the effect produced is concerned, not every action of a soul transcends an action of the nature of an inanimate thing. For the effect produced, that is, a natural mode of existing, and the things necessary for it, must be present in the case of inanimate bodies just as they are in the case of animate ones. But in the case of inanimate bodies, the effect is brought about by an extrinsic agent, whereas in the case of animate bodies, it is caused by an intrinsic agent. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 7.) The actions to which the powers of a vegetative soul are directed are of this sort. (Cf. Aristotle, On the Soul 2.4, 416a18.) For the generative power is directed to giving existence to the individual thing; the augmentative power, to giving the thing its proper size; and the nutritive power, to preserving the thing in existence. (Cf. Aristotle, On the Soul 2.4, 416b11–13; Aquinas, Commentary on Aristotle’s On the Soul, bk. 1, lect. 14; bk. 2, lect. 5 and 9; On Evil, q. 5, a. 5, obj. 6; Commentary on Aristotle’s On the Heavens, bk. 2, lect. 10, n. 391.) But in inanimate things these effects are brought about only by an extrinsic agent. For this reason, the aforementioned powers of a soul are said to be natural.

However, there are other higher actions of a soul which transcend the actions of natural forms, and also the effects produced by them, seeing that all things are disposed by nature to exist in the soul with an immaterial existence. For the human soul, in a certain respect, is all things by sensing and understanding. (Cf. Aristotle, On the Soul 3.8, 431b21.) Moreover, there must be different grades of such immaterial existence.

For there is one grade inasmuch as things exist in the soul without their proper matter, but with the singularity and individuating conditions which are the result of matter. This is the grade of sense, which is receptive of individual species without matter, yet receives them in a bodily organ. (Cf. Aristotle, On the Soul 2.12, 424a18; Averroes, Commentary on Aristotle’s On the Soul, bk. 2, comm. 121; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 24.)

Now the intellect which receives species completely abstracted from matter and material conditions, and without a bodily organ, constitutes a higher and more perfect grade of immateriality. (Cf. Aristotle, On the Soul 3.4, 430a6–9.)

Furthermore, just as a thing has a natural inclination toward something, and has movement and action in order to pursue that toward which it is inclined through its natural form, so also does the inclination toward a thing apprehended by sense or by intellect follow upon the apprehension of a sensible or intelligible form. (Cf. Aristotle, On the Soul 3.10, 433b10–12; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 5.) This inclination belongs to the appetitive power. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 5.) And again, as a consequence of this, there must be some movement by which it attains the thing desired. This pertains to the motive power.

Moreover, five things are required for the perfect sense knowledge which an animal should have.

First, that sense receive species from sensible things and this pertains to the proper sense.

Second, that the animal make some judgment about the sensible qualities received and distinguish them one from another, and this must be done by a power to which all sensible qualities are related. (Cf. Aristotle, On the Soul 3.2, 426b20–23; 427a9–14; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 13 and 27; ST I.78.4, resp.; Avicenna, De anima, part 4, ch. 2; Averroes, Commentary on Aristotle’s On the Soul, bk. 3, comm. 7.) This power is called the common sense.

Third, that the species of sensible things which have been received be retained. Now an animal needs to apprehend sensible things not only when they are present, but also after they have disappeared. And it is necessary that this also be attributed to some power. For in corporeal things there is one principle that receives, and another that retains, because things which are good recipients are sometimes poor retainers. (Cf. Aquinas, Commentary on Aristotle’s On Memory and Recollection, tract. 2, ch. 1.) This power is called imagination or “fantasy.” (Cf. Aristotle, On the Soul 3.3, 428b10–429a2; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 4; Avicenna, De anima, part 1, ch. 5.)

In the fourth place, the animal must know certain intentions which sense does not apprehend, such as the harmful, the useful, and so on. Man, indeed, acquires a knowledge of these by investigation and by inference, but other animals, by a certain natural instinct. (Cf. Aquinas, Commentary on the Nicomachean Ethics, bk. 3, lect. 19.) For example, the sheep flees naturally from the wolf as something harmful. Hence, in animals other than man a natural estimative power is directed to this end, but in man there is a cogitative power which collates particular intentions. (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 13 and 28; Commentary on Aristotle’s On Memory and Recollection, tract. 2, ch. 2.) This is why it is called both particular reason and passive intellect. (Cf. Aristotle, On the Soul 3.5, 430a24–25; Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 4, n. 745.)

In the fifth place, it is necessary that those things which were first apprehended by sense and conserved interiorly be recalled again to actual consideration. This belongs to a memorative power, which operates without any investigation in the case of some animals, but with investigation and study in the case of men. Therefore, in men there is not only memory but also reminiscence. (Aristotle, On Memory and Recollection 2.2, 453a4–14; Avicenna, De anima, part 4, ch. 3; Aquinas, Commentary on Aristotle’s On Memory and Recollection, tract. 2, ch. 5.) Moreover, it was necessary that a power distinct from the others be directed to this end, because the activity of the other sensitive powers entails a movement from things to the soul, whereas the activity of the memorative power entails an opposite movement from the soul to things. But diverse movements require diverse motive principles, and motive principles are called powers.

Now because the proper sense, which is first in the order of sensitive powers, is changed immediately by sensible objects, it was necessary for it to be divided into different powers in accordance with the diversity of sensible modifications. (Cf. ST I.78.3, resp.) For the grade and order of modifications by which the senses are altered by sensible qualities must be considered in relation to immaterial modifications, because sense is receptive of sensible species without matter.

Hence, there are some sensible objects whose species, although they are received immaterially in the senses, still cause a material modification in sensitive animals. Now qualities which are also principles of change in material things are of this sort, for instance, hot and cold, wet and dry, and the like. (Cf. Aristotle, On the Soul 2.11, 423b26–29; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 14 and 23; Commentary on Aristotle’s On Sense and What Is Sensed, tract. 1, ch. 4.) Hence, because sensible qualities of this kind also modify us by acting upon us, (Cf. Aristotle, On the Soul 2.11, 423b12–16; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 23.) and because material modification is made by contact, it was necessary that such sensible qualities be sensed by making contact with them. (Cf. Aristotle, On the Soul 3.13, 435a17.) This is the reason why the sensory power experiencing such qualities is called touch.

However, there are some sensible qualities which do not, indeed, change us materially, although their mutation has a material change connected with it. This occurs in two ways.

First, in the way that the material change affects the sensible quality as well as the one sensing. This pertains to taste. (Cf. Aristotle, On the Soul 2.10, 422a8–b16.) For, although the taste of a thing does not change the sense organ by making it the tasted thing itself, nevertheless this modification does not occur without some change taking place in the thing tasted as well as in the organ of taste, and particularly as a result of moisture.

Second, in the way that the material change affects the sensible quality alone. Now change of this sort is caused either by a dissipation and alteration of the sensible object, as occurs, for instance, in the sense of smell, (Cf. Aristotle, On the Soul 2.9, 421a7–b8.) or by a local change only, (Cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 16.) as occurs in the case of hearing. (Cf. Aristotle, On the Soul 2.9, 419b4–421a6.) So it is that hearing and smell sense not by contact with an object, but through an extrinsic medium, because they occur without a material change on the side of the one sensing, although material change does take place in the sensible object. However, taste alone senses by contact because it requires a material modification in the one sensing. (Cf. Aristotle, On the Soul 2.10, 422a8; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 5.)

Furthermore, there are other sensible things which modify a sense without a material change being involved, such as light and color, and the sense which apprehends these is sight. Hence, sight is the noblest of all the senses and extends to more objects than the other senses do, because the sensible qualities perceived by it are common both to corruptible and incorruptible bodies. (Cf. Aristotle, On the Soul 2.7, 418a26–b26; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 14, n. 417; bk. 2, lect. 30, n. 668; Commentary on Aristotle’s On Sense and What Is Sensed, tract. 1, ch. 5, n. 77; SCG III.53; ST I.78.3, resp.; I-II.83.4, obj. 3.)

Similarly, the appetitive power, (Cf. Aristotle, On the Soul 2.3, 414b1–2; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 5; ST I-II.8.1, resp.) which follows the apprehension of the senses, must be divided in two ways. (Cf. Aristotle, On the Soul 3.9, 432b6; Plato, Timaeus 41c; 71b; Republic, bk. 4, 439d–441c; Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 8; SCG II.47.) For a thing is appetible either because it is delightful and suitable to the senses, and the concupiscible power is directed to this; (Cf. Aristotle, On the Soul 3.10, 433a25–26.) or because the capacity of enjoying things delightful to the senses is made possible through it, which sometimes occurs together with something that is displeasing to sense—for instance, when an animal by fighting makes possible the enjoyment of something properly delightful by driving away anything that hinders this. The irascible power is directed to this end. (Cf. Aristotle, Nicomachean Ethics 7.6, 1149a25–b2; On the Soul 3.9, 432b6; Aquinas, Commentary on Aristotle’s On the Soul, bk. 3, lect. 8.)

Moreover, since the motive power is directed to local movement, it is diversified only with respect to different local movements. (Cf. Aristotle, On the Soul 3.10, 433a13.) These movements may differ for different animals, since some of them are able to crawl, some to fly, some to walk, and some to move in other ways; or they may differ for different parts of one and the same animal because the particular parts of the body have their own movements.

Again, the grades of intellectual powers are similarly distinguished into cognitive and appetitive. (Cf. ST I.80.2.) Moreover, movement is common to sense and to the intellect, for the same body is moved by each of these powers through one and the same movement. Again, intellectual cognition requires two powers, namely, the agent intellect and the potential intellect, as is clear from the previous articles. (See above: qq. 3–5.)

Consequently, it is obvious that there are three grades of powers in the soul, namely, the vegetative, sensitive, and rational. Moreover, there are five genera of powers, that is, the nutritive, sensitive, intellective, appetitive, and locomotive, and each of these contains many powers under itself, as has been pointed out. (Cf. Aristotle, On the Soul 2.3, 414a31–32; 2.2, 413b10–15; Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 5 and 7; On Truth, q. 10, a. 1, ad 2; ST I.78.1.)

Reply Obj. 1: Contraries are the things which differ most from each other, but within the same genus. (Cf. John of Rupella, Summa de anima, bk. 2, ch. 61 [II].) Moreover, objects different in genus befit diverse powers because a genus is also potential in a certain respect. (Cf. Aristotle, Metaphysics 10.8, 1058a20–25; Aquinas, Commentary on Aristotle’s Metaphysics, bk. 10, lect. 10.) Therefore, contraries are related to one and the same power.

Reply Obj. 2: Although sound and color differ as accidents, yet they differ essentially so far as the alteration which they produce in sense is concerned, as has been explained. (See above: resp.) However, a man and a stone do not, because sense is modified in the same way by them. Therefore, a man and a stone differ accidentally so far as they are sensed, although they differ substantially as substances. For nothing prevents a difference from being related substantially to one genus, and accidentally to another, as white and black differ essentially in the genus of color, but not in that of substance.

Reply Obj. 3: The same thing is not related to different powers of the soul, according to the same formal object, but according to different objects.

Reply Obj. 4: The higher a power, the more numerous are the things to which it extends. (Cf. Aquinas, On Truth, q. 15, a. 2, ad 7; q. 2, a. 3, s.c. 5.) Hence, the formal object of such a power has greater scope. This is why certain things that convene in the formal object of a superior power are separated from each other in the formal object of inferior powers.

Reply Obj. 5: Habits are not perfections of powers as though powers existed for the sake of habits, but habits exist for the sake of powers in order that powers may better attain their objects. For this reason, powers are not distinguished by habits, but by objects, just as things made by art are not distinguished by objects but by ends.

Reply Obj. 6: Powers do not exist for the sake of organs, but vice versa. (Cf. ST I.78.3, resp.) Consequently, organs are distinguished from one another by objects rather than the reverse.

Reply Obj. 7: A soul has some particular end, just as the human soul has an intelligible good as its end. (Cf. Aristotle, Nicomachean Ethics 10.7, 1178a1–9; Aquinas, Commentary on the Nicomachean Ethics, bk. 10, lect. 11.) Besides, it also has other ends ordered to this ultimate end, just as the sensible is ordered to the intelligible. And because the soul is directed to its object through its powers, it also follows that in man the sensitive power exists for the sake of the intellective, and so on. Thus, with respect to the account of the end, one power arises from another because of the relationship of their objects. (Cf. Aquinas, In I Sent., d. 3, q. 4, a. 3; In II Sent., d. 24, q. 1, a. 2; In IV Sent., d. 44, q. 3, a. 3, resp. 1; ST I.77.7.) Hence, the distinction between the powers of the soul from the point of view of origin and that of objects involves no opposition.

Reply Obj. 8: Although an accident by its very nature cannot be the subject of another accident, nevertheless a subject is determined by one accident through the intermediary of another, just as a body is subject to color through the medium of its surface. (Cf. Aristotle, Metaphysics 4.4, 1007b2–4; Aquinas, Commentary on Aristotle’s Metaphysics, bk. 4, lect. 7, nn. 629–36; bk. 5, lect. 19, nn. 1054–58.) Thus, one accident proceeds from its subject through the medium of another accident, and one power of the soul proceeds from its essence through the medium of another power.

Reply Obj. 9: The soul by one power can bring itself to bear on more objects than a natural thing can, just as sight apprehends all visible objects. But the soul, by reason of its nobility, performs many more operations than inanimate things do, and, therefore, must have several powers.

Reply Obj. 10: The order among the soul’s powers is according to the order among their objects. (Cf. ST I.77.4.) But order can be observed in both, either in relation to perfection—and in this case the intellect is prior to sense—or in relation to the process of generation, and in this case sense is prior to the intellect. For in the process of generation an accidental disposition is induced prior to the substantial form.

Reply Obj. 11: The intellect naturally desires the intelligible as such. For the intellect by nature desires to know, and sense desires to sense. But there must be an appetitive power in addition to sense and intellect, because the sensible or intelligible object is desired not merely in order that it may be sensed and understood, but also for some other end. Therefore, there must be an appetitive power in addition to sense and intellect.

Reply Obj. 12: The will exists in the intellective order inasmuch as it follows the apprehension of the intellect. (Cf. Aristotle, On the Soul 3.10, 433a24; Aquinas, Commentary on the Nicomachean Ethics, bk. 3, lect. 1.) Indeed, the will belongs to the same grade of operation, namely, operations of the soul, but not to the same genus. (Cf. Aristotle, On the Soul 3.9, 432b5; Aquinas, Commentary on the Nicomachean Ethics, bk. 3, lect. 4.) The same thing must be said for the irascible and concupiscible appetite in relation to sense.

Reply Obj. 13: The intellect and appetite cause movement inasmuch as they command movement. But there must exist a motive power which executes movement according as the members of the body follow the command of appetite, intellect, or sense.

Reply Obj. 14: The powers of the vegetative soul are called natural powers because they operate only as nature does in bodies. But they are called powers of a soul because such powers do the things that nature does in a more superior way, as was previously shown. (See above: resp.)

Reply Obj. 15: A real inanimate being receives its species and proper size at the same time. This is not possible in living things which require the least possible size at the beginning of generation, because they are generated from semen. Therefore, in addition to the generative power which these things possess, there must exist also an augmentative power which produces their proper size. Moreover, this must occur in view of the fact that something is changed within a substance by augmentation and is added to that substance. Furthermore, this change is brought about by heat, which transforms both what is taken in from without, and also what exists within the thing itself. Hence, a nutritive power is necessary for the conservation of the individual in order that whatever is lost may be continually restored, that whatever is lacking for the completion of its size may be added, and that whatever is necessary for the generation of semen may be produced. This nutritive power serves both the augmentative and the generative power, and thereby preserves the individual in existence.

Reply Obj. 16: Sound and color and things of this sort differ according to the different way in which they modify sense. However, they are not sensible things of different genera. Therefore, the sensory powers are not differentiated by them.

Reply Obj. 17: In On the Soul 2 the Philosopher concludes that touch is not one sense but many, because the contraries which touch experiences are not brought together under one and the same genus, as the different contraries which can be considered in visible things are brought together under one and the same genus of color. (Aristotle, On the Soul 2.6, 418a14; 2.11, 422b17–33; cf. Aquinas, Commentary on Aristotle’s On the Soul, bk. 2, lect. 22; Averroes, Commentary on Aristotle’s On the Soul, bk. 2, comm. 108.) Nevertheless, all are alike in this respect, that they do not sense through an external medium, and all are called touch, so that there is one sense in genus, divided into several species. However, it could be said that there is one sense pure and simple because all the contraries of which touch is cognitive are known of themselves, for they are known alternately and brought together under one genus, although this is unnamed, since the proximate genus both of heat and of cold is unnamed.

Reply Obj. 18: Since the powers of the soul are properties of it, memory is not prevented from being a power distinct from a first sense, because memory is said to be a passion of a first sense. This statement shows the way in which memory is related to sense.

Reply Obj. 19: Sense receives the species of sensible things in the organs of the body and perceives singulars. However, the intellect receives the species of things without a bodily organ and is cognizant of universals. Hence, a diversity of objects requires a diversity of powers in the sensitive part, which does not require a diversity of powers in the intellective part. (Cf. Aquinas, On Truth, q. 15, a. 2, resp.) For in material things, reception and retention are not one and the same, whereas in immaterial things these activities are one and the same. It is also necessary to distinguish the senses from one another with respect to the different modes of change involved. But this is unnecessary in the case of the intellect.

Reply Obj. 20: The same object, namely, the intelligible species in act, is related to the agent intellect as that which is produced by this intellect, and to the potential intellect as that which moves the potential intellect. (Cf. Aquinas, On Truth, q. 15, a. 2, resp.) Thus, it is obvious that the same thing is not related in the same respect both to the agent intellect and to the potential intellect.