habits, but only those which arise from acts which give them the special character of stability. Hence mere _opinion_ in the intellectual order, as distinct from _science_, or a mere _inclination_ resulting from a few isolated acts, as distinct from a _virtue_ or a _vice_ in the moral order, are not habits.(338) Habits, therefore, belong properly to the faculties of a spiritual substance; indirectly, however, they extend their influence to the lower or organic powers dependent on, and controlled by, the spiritual faculties. To the various dispositions and facilities of action acquired by animals through “training,” “adaptation,” “acclimatization,” etc., we may apply what has been said in regard to the sense faculties and executive powers of the human body. Just as we may regard the internal sense faculties (memory, imagination, sense appetite) in man as in a secondary and subordinate way subjects of habits, in so far as these faculties act under the direction and control of human reason and will,(339) so also the organic dispositions induced in irrational animals by the direction and guidance of human reason may indeed be regarded as extensions or effects of the habits that dispose the rational human faculties, but not as themselves in the strict sense habits.(340) If, then, habits belong properly to intellect and will, and if their function is to dispose or indispose the human agent for the attainment of the perfection in which his last end consists, we must naturally look to _Psychology_ and _Ethics_ for a detailed analysis of them. Here we must be content with a word on their origin, their effects, and their importance. Habits are produced by acts. The act modifies the faculty. If, for instance, nothing remained in our cognitive faculties after each transient cognitive act had passed, memory would be inexplicable and knowledge impossible; nor could the repetition of any act ever become easier than its first performance. This something that remains is a habit, or the beginning of a habit A habit may be produced by a single act: the mind’s first intuition of an axiom or principle produces a _habit or habitual knowledge_ of that principle. But as a rule it requires a repetition of any act, and that for a long time at comparatively short intervals, to produce a _habit_ of that act, a stable disposition whereby it can be readily repeated; and to strengthen and perfect the habit the acts must be formed with a growing degree of intensity and energy. Progress in virtue demands sustained and increasingly earnest efforts.