Thus, then, if we speak of habit as a disposition of the subject in relation to form or nature, it may be natural in either of the foregoing ways.  For there is a certain natural disposition demanded by the human species, so that no man can be without it.  And this disposition is natural in respect of the specific nature.  But since such a disposition has a certain latitude, it happens that different grades of this disposition are becoming to different men in respect of the individual nature.  And this disposition may be either entirely from nature, or partly from nature, and partly from an extrinsic principle, as we have said of those who are healed by means of art.

But the habit which is a disposition to operation, and whose subject is a power of the soul, as stated above (Q. 50, A. 2), may be natural whether in respect of the specific nature or in respect of the individual nature:  in respect of the specific nature, on the part of the soul itself, which, since it is the form of the body, is the specific principle; but in respect of the individual nature, on the part of the body, which is the material principle.  Yet in neither way does it happen that there are natural habits in man, so that they be entirely from nature.  In the angels, indeed, this does happen, since they have intelligible species naturally impressed on them, which cannot be said of the human soul, as we have said in the First Part (Q. 55, A. 2; Q. 84, A. 3).

There are, therefore, in man certain natural habits, owing their existence, partly to nature, and partly to some extrinsic principle:  in one way, indeed, in the apprehensive powers; in another way, in the appetitive powers.  For in the apprehensive powers there may be a natural habit by way of a beginning, both in respect of the specific nature, and in respect of the individual nature.  This happens with regard to the specific nature, on the part of the soul itself:  thus the understanding of first principles is called a natural habit.  For it is owing to the very nature of the intellectual soul that man, having once grasped what is a whole and what is a part, should at once perceive that every whole is larger than its part:  and in like manner with regard to other such principles.  Yet what is a whole, and what is a part—­this he cannot know except through the intelligible species which he has received from phantasms:  and for this reason, the Philosopher at the end of the Posterior Analytics shows that knowledge of principles comes to us from the senses.

But in respect of the individual nature, a habit of knowledge is natural as to its beginning, in so far as one man, from the disposition of his organs of sense, is more apt than another to understand well, since we need the sensitive powers for the operation of the intellect.

In the appetitive powers, however, no habit is natural in its beginning, on the part of the soul itself, as to the substance of the habit; but only as to certain principles thereof, as, for instance, the principles of common law are called the “nurseries of virtue.”  The reason of this is because the inclination to its proper objects, which seems to be the beginning of a habit, does not belong to the habit, but rather to the very nature of the powers.