I answer that, As we have said above (Q[49], AA[2],3), habit implies a certain disposition in relation to nature or to operation. If therefore we take habit as having a relation to nature, it cannot be in the soul---that is, if we speak of human nature: for the soul itself is the form completing the human nature; so that, regarded in this way, habit or disposition is rather to be found in the body by reason of its relation to the soul, than in the soul by reason of its relation to the body. But if we speak of a higher nature, of which man may become a partaker, according to 2 Pet. 1, "that we may be partakers of the Divine Nature": thus nothing hinders some habit, namely, grace, from being in the soul in respect of its essence, as we shall state later on (Q[110], A[4]).
On the other hand, if we take habit in its relation to operation, it is chiefly thus that habits are found in the soul: in so far as the soul is not determined to one operation, but is indifferent to many, which is a condition for a habit, as we have said above (Q[49], A[4]). And since the soul is the principle of operation through its powers, therefore, regarded in this sense, habits are in the soul in respect of its powers.
Reply to Objection 1: The essence of the soul belongs to human nature, not as a subject requiring to be disposed to something further, but as a form and nature to which someone is disposed.
Reply to Objection 2: Accident is not of itself the subject of accident. But since among accidents themselves there is a certain order, the subject, according as it is under one accident, is conceived as the subject of a further accident. In this way we say that one accident is the subject of another; as superficies is the subject of color, in which sense power is the subject of habit.
Reply to Objection 3: Habit takes precedence of power, according as it implies a disposition to nature: whereas power always implies a relation to operation, which is posterior, since nature is the principle of operation. But the habit whose subject is a power, does not imply relation to nature, but to operation. Wherefore it is posterior to power. Or, we may say that habit takes precedence of power, as the complete takes precedence of the incomplete, and as act takes precedence of potentiality. For act is naturally prior to potentiality, though potentiality is prior in order of generation and time, as stated in Metaph. vii, text. 17; ix, text. 13.
Whether there can be any habits in the powers of the sensitive parts?
Objection 1: It would seem that there cannot be any habits in the powers of the sensitive part. For as the nutritive power is an irrational part, so is the sensitive power. But there can be no habits in the powers of the nutritive part. Therefore we ought not to put any habit in the powers of the sensitive part.
Objection 2: Further, the sensitive parts are common to us and the brutes. But there are not any habits in brutes: for in them there is no will, which is put in the definition of habit, as we have said above (Q[49], A[3]). Therefore there are no habits in the sensitive powers.
Objection 3: Further, the habits of the soul are sciences and virtues: and just as science is related to the apprehensive power, so it virtue related to the appetitive power. But in the sensitive powers there are no sciences: since science is of universals, which the sensitive powers cannot apprehend. Therefore, neither can there be habits of virtue in the sensitive part.
On the contrary, The Philosopher says (Ethic. iii, 10) that "some virtues," namely, temperance and fortitude, "belong to the irrational part."
I answer that, The sensitive powers can be considered in two ways: first, according as they act from natural instinct: secondly, according as they act at the command of reason. According as they act from natural instinct, they are ordained to one thing, even as nature is; but according as they act at the command of reason, they can be ordained to various things. And thus there can be habits in them, by which they are well or ill disposed in regard to something.
Reply to Objection 1: The powers of the nutritive part have not an inborn aptitude to obey the command of reason, and therefore there are no habits in them. But the sensitive powers have an inborn aptitude to obey the command of reason; and therefore habits can be in them: for in so far as they obey reason, in a certain sense they are said to be rational, as stated in Ethic. i, 13.
Reply to Objection 2: The sensitive powers of dumb animals do not act at the command of reason; but if they are left to themselves, such animals act from natural instinct: and so in them there are no habits ordained to operations. There are in them, however, certain dispositions in relation to nature, as health and beauty. But whereas by man's reason brutes are disposed by a sort of custom to do things in this or that way, so in this sense, to a certain extent, we can admit the existence of habits in dumb animals: wherefore Augustine says (QQ. lxxxiii, qu. 36): "We find the most untamed beasts, deterred by fear of pain, from that wherein they took the keenest pleasure; and when this has become a custom in them, we say that they are tame and gentle." But the habit is incomplete, as to the use of the will, for they have not that power of using or of refraining, which seems to belong to the notion of habit: and therefore, properly speaking, there can be no habits in them.
Reply to Objection 3: The sensitive appetite has an inborn aptitude to be moved by the rational appetite, as stated in De Anima iii, text. 57: but the rational powers of apprehension have an inborn aptitude to receive from the sensitive powers. And therefore it is more suitable that habits should be in the powers of sensitive appetite than in the powers of sensitive apprehension, since in the powers of sensitive appetite habits do not exist except according as they act at the command of the reason. And yet even in the interior powers of sensitive apprehension, we may admit of certain habits whereby man has a facility of memory, thought or imagination: wherefore also the Philosopher says (De Memor. et Remin. ii) that "custom conduces much to a good memory": the reason of which is that these powers also are moved to act at the command of the reason.
On the other hand the exterior apprehensive powers, as sight, hearing and the like, are not susceptible of habits, but are ordained to their fixed acts, according to the disposition of their nature, just as the members of the body, for there are no habits in them, but rather in the powers which command their movements.
Whether there is any habit in the intellect?
Objection 1: It would seem that there are no habits in the intellect. For habits are in conformity with operations, as stated above (A[1]). But the operations of man are common to soul and body, as stated in De Anima i, text. 64. Therefore also are habits. But the intellect is not an act of the body (De Anima iii, text. 6). Therefore the intellect is not the subject of a habit.
Objection 2: Further, whatever is in a thing, is there according to the mode of that in which it is. But that which is form without matter, is act only: whereas what is composed of form and matter, has potentiality and act at the same time. Therefore nothing at the same time potential and actual can be in that which is form only, but only in that which is composed of matter and form. Now the intellect is form without matter. Therefore habit, which has potentiality at the same time as act, being a sort of medium between the two, cannot be in the intellect; but only in the "conjunction," which is composed of soul and body.
Objection 3: Further, habit is a disposition whereby we are well or ill disposed in regard to something, as is said (Metaph. v, text. 25). But that anyone should be well or ill disposed to an act of the intellect is due to some disposition of the body: wherefore also it is stated (De Anima ii, text. 94) that "we observe men with soft flesh to be quick witted." Therefore the habits of knowledge are not in the intellect, which is separate, but in some power which is the act of some part of the body.
On the contrary, The Philosopher (Ethic. vi, 2,3,10) puts science, wisdom and understanding, which is the habit of first principles, in the intellective part of the soul.
I answer that, concerning intellective habits there have been various opinions. Some, supposing that there was only one "possible" [*FP, Q[79], A[2], ad 2] intellect for all men, were bound to hold that habits of knowledge are not in the intellect itself, but in the interior sensitive powers. For it is manifest that men differ in habits; and so it was impossible to put the habits of knowledge directly in that, which, being only one, would be common to all men. Wherefore if there were but one single "possible" intellect of all men, the habits of science, in which men differ from one another, could not be in the "possible" intellect as their subject, but would be in the interior sensitive powers, which differ in various men.
Now, in the first place, this supposition is contrary to the mind of Aristotle. For it is manifest that the sensitive powers are rational, not by their essence, but only by participation (Ethic. i, 13). Now the Philosopher puts the intellectual virtues, which are wisdom, science and understanding, in that which is rational by its essence. Wherefore they are not in the sensitive powers, but in the intellect itself. Moreover he says expressly (De Anima iii, text. 8,18) that when the "possible" intellect "is thus identified with each thing," that is, when it is reduced to act in respect of singulars by the intelligible species, "then it is said to be in act, as the knower is said to be in act; and this happens when the intellect can act of itself," i.e. by considering: "and even then it is in potentiality in a sense; but not in the same way as before learning and discovering." Therefore the "possible" intellect itself is the subject of the habit of science, by which the intellect, even though it be not actually considering, is able to consider. In the second place, this supposition is contrary to the truth. For as to whom belongs the operation, belongs also the power to operate, belongs also the habit. But to understand and to consider is the proper act of the intellect. Therefore also the habit whereby one considers is properly in the intellect itself.
Reply to Objection 1: Some said, as Simplicius reports in his Commentary on the Predicaments, that, since every operation of man is to a certain extent an operation of the "conjunctum," as the Philosopher says (De Anima i, text. 64); therefore no habit is in the soul only, but in the "conjunctum." And from this it follows that no habit is in the intellect, for the intellect is separate, as ran the argument, given above. But the argument is no cogent. For habit is not a disposition of the object to the power, but rather a disposition of the power to the object: wherefore the habit needs to be in that power which is principle of the act, and not in that which is compared to the power as its object.
Now the act of understanding is not said to be common to soul and body, except in respect of the phantasm, as is stated in De Anima, text. 66. But it is clear that the phantasm is compared as object to the passive intellect (De Anima iii, text. 3,39). Whence it follows that the intellective habit is chiefly on the part of the intellect itself; and not on the part of the phantasm, which is common to soul and body. And therefore we must say that the "possible" intellect is the subject of habit, which is in potentiality to many: and this belongs, above all, to the "possible" intellect. Wherefore the "possible" intellect is the subject of intellectual habits.
Reply to Objection 2: As potentiality to sensible being belongs to corporeal matter, so potentiality to intellectual being belongs to the "possible" intellect. Wherefore nothing forbids habit to be in the "possible" intellect, for it is midway between pure potentiality and perfect act.