Thomas Aquinas

“ For instance, when a man is healed by himself, his health is entirely from nature; but when a man is healed by means of medicine, health is partly from nature, partly from an extrinsic principle.
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. ”

“ And since habits need to be in proportion with that to which man is disposed by them, therefore is it necessary that those habits, which dispose to this end, exceed the proportion of human nature. Wherefore such habits can never be in man except by Divine infusion, as is the case with all gratuitous virtues. ”

“ With regard then to the former passive principle, it is possible for a certain active principle to entirely overcome, by one act, the power of its passive principle: thus one self-evident proposition convinces the intellect, so that it gives a firm assent to the conclusion, but a probable proposition cannot do this. Wherefore a habit of opinion needs to be caused by many acts of the reason, even on the part of the "possible" intellect: whereas a habit of science can be caused by a single act of the reason, so far as the "possible" intellect is concerned. ”

“ 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. ”

“ I answer that, In the agent there is sometimes only the active principle of its act: for instance in fire there is only the active principle of heating. And in such an agent a habit cannot be caused by its own act: for which reason natural things cannot become accustomed or unaccustomed, as is stated in Ethic. ii, 1. But a certain agent is to be found, in which there is both the active and the passive principle of its act, as we see in human acts. ”

“ Something may be added even naturally to the nature of a power, while it cannot belong to the power itself. For instance, with regard to the angels, it cannot belong to the intellective power itself capable of knowing all things: for thus it would have to be the act of all things, which belongs to God alone. Because that by which something is known, must needs be the actual likeness of the thing known: whence it would follow, if the power of the angel knew all things by itself, that it was the likeness and act of all things. ”

“ Just as, therefore, sometimes, in order to show His power, He causes health, without its natural cause, but which nature could have caused, so also, at times, for the manifestation of His power, He infuses into man even those habits which can be caused by a natural power. ”

“ That God works in all according to their mode, does not hinder God from doing what nature cannot do: but it follows from this that He does nothing contrary to that which is suitable to nature.
Reply to Objection 3: Acts produced by an infused habit, do not cause a habit, but strengthen the already existing habit; just as the remedies of medicine given to a man who is naturally health, do not cause a kind of health, but give new strength to the health he had before. ”

“ But in order that some quality be caused in that which is passive the active principle must entirely overcome the passive. Whence we see that because fire cannot at once overcome the combustible, it does not enkindle at once ”

“ Reply to Objection 2: The same thing, and in the same respect, cannot be mover and moved; but nothing prevents a thing from being moved by itself as to different respects, as is proved in Physics viii, text. ”