In the (unfinished) _Summa Theologiae_, the Ethical views and cognate questions occupy the two sections of the second part--the so-called _prima_ and _secunda secundae_. He begins, in the Aristotelian fashion, by seeking an ultimate end of human action, and finds it in the attainment of the highest good or happiness. But as no created thing can answer to the idea of the highest good, it must be placed in God. God, however, as the highest good, can only be the object, in the search after human happiness, for happiness in itself is a state of the mind or act of the soul. The question then arises, "what sort of act?" Does it fall under the Will or under the Intelligence? The answer is, Not under the will, because happiness is neither desire nor pleasure, but _consecutio_, that is, a possessing. Desire precedes _consecutio_, and pleasure follows upon it; but the act of getting possession, in which lies happiness, is distinct from both. This is illustrated by the case of the miser having his happiness in the mere possession of money; and the position is essentially the same as Butler's, in regard to our appetites and desires, that they blindly seek their objects with no regard to pleasure. Thomas concludes that the _consecutio_, or happiness, is an act of the intelligence; what pleasure there is being a mere accidental accompaniment.
Distinguishing between two phases of the intellect--the theoretic and the practical--in the one of which it is an end to itself, but in the other subordinated to an external aim, he places true happiness in acts of the self-sufficing theoretic intelligence. In this life, however, such a constant exercise of the intellect is not possible, and accordingly what happiness there is, must be found, in great measure, in the exercise of the practical intellect, directing and governing the lower desires and passions. This twofold conception of happiness is Aristotelian, even as expressed by Thomas under the distinction of perfect and imperfect happiness; but when he goes on to associate perfect happiness with the future life only, to found an argument for a future life from the desire of a happiness more perfect than can be found here, and to make the pure contemplation, in which consists highest bliss, a vision of the divine essence face to face, a direct cognition of Deity far surpassing demonstrative knowledge or mortal faith--he is more theologian than philosopher, or if a philosopher, more Platonist than Aristotelian.