Summa Theologiae Moralis, vol. I: De Principiis

S. Th. I-II, q. 51, 52, 53; q. 63, a. 1 and 2; De Virt. q. 1, a. 8 and 9.

566. Principle I. One operative habit of the soul is in man from nature, not indeed totally (then it would be innate) but partially and according to a beginning, namely the habit of first principles, inasmuch as, the terms being known through intelligible species (which are not in us from nature), at once the facility results of seeing that the terms agree with each other or not.

567. Principle II. Other habits are caused in the soul from the human acts proper to the agent, namely from the acts of the moving potency in the moved potency of the same agent¹; thus e.g. the act of the appetitive virtue proceeds from an apprehension representing the object, the intellective power as reasoning has the active principle of self-evident propositions, the possible intellect is moved by the agent intellect. For the agent in which there is at the same time the active and passive principle of its act, inasmuch as it is active can cause the habit, and inasmuch as it is passive can receive it and be perfected by it.

They are acquired habits².

Sometimes by one act the habit is caused, when the active potency by one act totally overcomes the passive potency, as happens in the habit of science because one act suffices for conviction³; — ordinarily however from acts of the same species repeated, as happens in the habit of opinion, in the habits of the internal senses, and especially in the moral virtues and vices, because reason by one act cannot make that the appetite is ordinarily, and generally, and in all circumstances good or evil, as is required for virtue or vice.

568. Principle III. Other habits are caused by God, namely supernatural ones by which we are disposed to a supernatural end exceeding the capacity of human nature; likewise God can also cause habits which by our acts we can acquire, as he gave some the knowledge of the Scriptures or of languages.

They are infused habits of themselves, or accidentally.

569. Principle IV. No habit is innate. — Supernatural habits are in no way in us from nature; — nor are acquired habits from nature according to essence, perfection, and consummation; but only according to a certain aptitude and beginning, and indeed in two ways.

a) On the part of the soul, not according to the beginning of the habit itself, but only according to aptitude or as to its principles, inasmuch as the intellect and will naturally say the order and inclination to the knowledge of truth and love of good, and thus the habits of first principles in the intellect and the natural inclination of the will to good are the principles or seeds from which intellectual and moral virtues are generated⁴. But « because the inclination to proper objects, which seems to be the beginning of habit, does not pertain to the habit but rather to the very notion of the potencies » (q. 51, a. 1), therefore it is not the beginning of the habit itself according to itself, but only according to its principles or according to its aptitude in causes.

b) On the part of the body and internal senses, also according to the beginning of the habit itself, inasmuch as because of their disposition man is helped or impeded for good, and thus is better or less well disposed for certain habits: thus from the disposition of the organs and complexion of the body, one is more disposed for understanding than another, or has a propensity for certain virtues (chastity, fortitude, meekness) or vices (anger, lust). Thus he has greater aptitude for receiving such or such a habit and will more easily acquire it⁵.

Moreover habits of the body can be caused by one act, if the producing cause is of great strength, as health from one strong medicine, organic deformation from one passion, e.g. a great terror.

570. Principle V. Habits are increased, but not by addition of a new degree: for if added, two or more would be added, whence there would be more habits and thus more accidents of the same species in the same subject, which is repugnant (e.g. two charities, two temperances, two arts); nor would the former habit truly become greater and be increased, but rather be multiplied. But they are increased

1°) according to themselves: extensively, inasmuch as the same habit in number extends itself to new objects to which it was not before ordered; as theological knowledge is extended by the study of a new treatise;

2°) on the part of the subject: intensively, inasmuch as the same habit is more received and adheres more firmly in the subject, and reduces it more to act; and accordingly the potency in which the habit resides more participates the character of habit, whence it tends more expeditely and promptly to act; as knowledge of the same treatise which becomes clearer. And indeed:

a) Habits are increased intensively by the same cause by which they are produced: for similar acts cause habits not only in species but also in degree and similar intensity; whence an act more intense or equally intense as the habit increases it or at least disposes to increase; but when the will does not use the habit totally and produces a less intense act, that act rather disposes to the diminution of the habit and does not increase it.

b) Habits are increased extensively by acts about another part of the object: he who already has knowledge of all the treatises of theology, one excepted, increases the habit by the study of that part.

571. Principle VI. Habits are corrupted of themselves or accidentally: accidentally, when the subject in which the habit is, is corrupted; of themselves i.e. by their contrary. It is to be noted that every habit which is acquired by one act, is corrupted by one act; but that which is acquired by many acts, is not corrupted except by many, but by one only is diminished.

Of themselves those habits which have no contrary are not corrupted, as the habit of principles. Those which have a contrary can be corrupted of themselves, as science and opinion by an opposite principle or by a sophistic deduction; and acquired moral virtue by contrary judgments of practical reason from ignorance, passion, or malice; likewise habits of the body.

Habits of the intellect and will are not corrupted accidentally, because these faculties are incorruptible; but habits of the sensitive potencies and of the body are corrupted, as temperance before the resurrection.

572. Principle VII. Habits are diminished intensively and extensively from the same cause by which they are corrupted of themselves, i.e. by their contrary, because diminution is the way to corruption.

Moreover some habits are also diminished and corrupted by the mere cessation from act, not indeed directly of themselves, but indirectly accidentally, namely by the removal of the hindrance, inasmuch as this cessation takes away the acts which prevented contraries from corrupting or diminishing the habit of themselves.