The condition of perfect happiness being a theoretic or intellectual state, the _visio_, and not the _delectatio_, is consistently given as its central fact; and when he proceeds to consider the other questions of Ethics, the same superiority is steadily ascribed to the intellectual function. It is because we _know_ a thing to be good that we wish it, and knowing it, we cannot help wishing. Conscience, as the name implies, is allied to knowledge. Reason gives the law to will.
After a long disquisition about the passions and the whole appetitive side of human nature, over which Reason is called to rule, he is brought to the subject of virtue. He is Aristotelian enough to describe virtue as _habitus_--a disposition or quality (like health) whereby a subject is more or less well disposed with reference to itself or something else; and he takes account of the acquisition of good moral habits (_virtutes acquisitae_) by practice. But with this he couples, or tends to substitute for it, the definition of Augustin that virtue is a good quality of mind, _quam Deus in nobis sine nobis operatur_, as a ground for _virtutes infusae_, conferred as gifts upon man, or rather on certain men, by free grace from on high. He wavers greatly at this stage, and in this respect his attitude is characteristic for all the schoolmen.
So again in passing from the general question of Virtue to the virtues, he puts several of the systems under contribution, as if not prepared to leave the guidance of Aristotle, but feeling at the same time the necessity of bridging over the distance between his position and Christian requirements. Understanding Aristotle to make a co-ordinate division of virtues into Moral and Intellectual, he gives reasons for such a step. Though virtue, he says, is not so much the perfecting of the operation of our faculties, as their employment by the will for good ends, it may be used in the first sense, and thus the intellectual virtues will be the habits of intelligence that procure the truest knowledge. The well-known division of the cardinal virtues is his next theme; and it is established as complete and satisfactory by a twofold deduction. But a still higher and more congenial view is immediately afterwards adopted from Plotinus. This is the Neo-Platonic description of the four virtues as _politicae, purgatoriae_, and _purgati animi_, according to the scale of elevation reached by the soul in its efforts to mount above sense. They are called by Thomas also _exemplares_, when regarded at once as the essence of the Deity, and as the models of human perfections.