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 Obj. 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 Obj. 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 Obj. 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. ________________________

THIRD ARTICLE [I-II, Q. 50, Art. 3]

Whether There Can Be Any Habits in the Powers of the Sensitive Part?

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.

Obj. 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.

Obj. 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.”