On the contrary, The Philosopher (Ethic. ii, 1,2) teaches that habits of virtue and vice are caused by acts.
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. For the acts of the appetitive power proceed from that same power according as it is moved by the apprehensive power presenting the object: and further, the intellective power, according as it reasons about conclusions, has, as it were, an active principle in a self-evident proposition. Wherefore by such acts habits can be caused in their agents; not indeed with regard to the first active principle, but with regard to that principle of the act, which principle is a mover moved. For everything that is passive and moved by another, is disposed by the action of the agent; wherefore if the acts be multiplied a certain quality is formed in the power which is passive and moved, which quality is called a habit: just as the habits of moral virtue are caused in the appetitive powers, according as they are moved by the reason, and as the habits of science are caused in the intellect, according as it is moved by first propositions.
Reply to Objection 1: The agent, as agent, does not receive anything. But in so far as it moves through being moved by another, it receives something from that which moves it: and thus is a habit caused.
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. 28,29.
Reply to Objection 3: The act which precedes the habit, in so far as it comes from an active principle, proceeds from a more excellent principle than is the habit caused thereby: just as the reason is a more excellent principle than the habit of moral virtue produced in the appetitive power by repeated acts, and as the understanding of first principles is a more excellent principle than the science of conclusions.
Whether a habit can be caused by one act?
Objection 1: It would seem that a habit can be caused by one act. For demonstration is an act of reason. But science, which is the habit of one conclusion, is caused by one demonstration. Therefore habit can be caused by one act.
Objection 2: Further, as acts happen to increase by multiplication so do they happen to increase by intensity. But a habit is caused by multiplication of acts. Therefore also if an act be very intense, it can be the generating cause of a habit.
Objection 3: Further, health and sickness are habits. But it happens that a man is healed or becomes ill, by one act. Therefore one act can cause a habit.
On the contrary, The Philosopher (Ethic. i, 7): "As neither does one swallow nor one day make spring: so neither does one day nor a short time make a man blessed and happy." But "happiness is an operation in respect of a habit of perfect virtue" (Ethic. i, 7,10,13). Therefore a habit of virtue, and for the same reason, other habits, is not caused by one act.
I answer that, As we have said already (A[2]), habit is caused by act, because a passive power is moved by an active principle. 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; but it gradually expels contrary dispositions, so that by overcoming it entirely, it may impress its likeness on it. Now it is clear that the active principle which is reason, cannot entirely overcome the appetitive power in one act: because the appetitive power is inclined variously, and to many things; while the reason judges in a single act, what should be willed in regard to various aspects and circumstances. Wherefore the appetitive power is not thereby entirely overcome, so as to be inclined like nature to the same thing, in the majority of cases; which inclination belongs to the habit of virtue. Therefore a habit of virtue cannot be caused by one act, but only by many.
But in the apprehensive powers, we must observe that there are two passive principles: one is the "possible" [*See FP, Q[79], A[2] ad 2] intellect itself; the other is the intellect which Aristotle (De Anima iii, text. 20) calls "passive," and is the "particular reason," that is the cogitative power, with memory and imagination. 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. But with regard to the lower apprehensive powers, the same acts need to be repeated many times for anything to be firmly impressed on the memory. And so the Philosopher says (De Memor. et Remin. 1) that "meditation strengthens memory." Bodily habits, however, can be caused by one act, if the active principle is of great power: sometimes, for instance, a strong dose of medicine restores health at once.
Hence the solutions to the objections are clear.
Whether any habits are infused in man by God?
Objection 1: It would seem that no habit is infused in man by God. For God treats all equally. If therefore He infuses habits into some, He would infuse them into all: which is clearly untrue.
Objection 2: Further, God works in all things according to the mode which is suitable to their nature: for "it belongs to Divine providence to preserve nature," as Dionysius says (Div. Nom. iv). But habits are naturally caused in man by acts, as we have said above (A[2]). Therefore God does not cause habits to be in man except by acts.
Objection 3: Further, if any habit be infused into man by God, man can by that habit perform many acts. But "from those acts a like habit is caused" (Ethic. ii, 1,2). Consequently there will be two habits of the same species in the same man, one acquired, the other infused. Now this seems impossible: for the two forms of the same species cannot be in the same subject. Therefore a habit is not infused into man by God.
On the contrary, it is written ( Ecclus. 15:5 ): "God filled him with the spirit of wisdom and understanding." Now wisdom and understanding are habits. Therefore some habits are infused into man by God.
I answer that, Some habits are infused by God into man, for two reasons.
The first reason is because there are some habits by which man is disposed to an end which exceeds the proportion of human nature, namely, the ultimate and perfect happiness of man, as stated above (Q[5], A[5]). 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.
The other reason is, because God can produce the effects of second causes, without these second causes, as we have said in the FP, Q[105], A[6]. 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. Thus He gave to the apostles the science of the Scriptures and of all tongues, which men can acquire by study or by custom, but not so perfectly.
Reply to Objection 1: God, in respect of His Nature, is the same to all, but in respect of the order of His Wisdom, for some fixed motive, gives certain things to some, which He does not give to others.
Reply to Objection 2: 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.