Secondly, it is evident from the fact that contemplation is sought principally for its own sake. But the act of the practical intellect is not sought for its own sake but for the sake of action: and these very actions are ordained to some end. Consequently it is evident that the last end cannot consist in the active life, which pertains to the practical intellect.
Thirdly, it is again evident, from the fact that in the contemplative life man has something in common with things above him, viz. with God and the angels, to whom he is made like by happiness. But in things pertaining to the active life, other animals also have something in common with man, although imperfectly.
Therefore the last and perfect happiness, which we await in the life to come, consists entirely in contemplation. But imperfect happiness, such as can be had here, consists first and principally, in an operation of the practical intellect directing human actions and passions, as stated in Ethic. x, 7, 8.
Reply Obj. 1: The asserted likeness of the practical intellect to God is one of proportion; that is to say, by reason of its standing in relation to what it knows, as God does to what He knows. But the likeness of the speculative intellect to God is one of union and "information"; which is a much greater likeness. And yet it may be answered that, in regard to the principal thing known, which is His Essence, God has not practical but merely speculative knowledge.
Reply Obj. 2: The practical intellect is ordained to good which is outside of it: but the speculative intellect has good within it, viz. the contemplation of truth. And if this good be perfect, the whole man is perfected and made good thereby: such a good the practical intellect has not; but it directs man thereto.
Reply Obj. 3: This argument would hold, if man himself were his own last end; for then the consideration and direction of his actions and passions would be his happiness. But since man's last end is something outside of him, to wit, God, to Whom we reach out by an operation of the speculative intellect; therefore, man's happiness consists in an operation of the speculative intellect rather than of the practical intellect. ________________________
SIXTH ARTICLE [I-II, Q. 3, Art. 6]
Whether Happiness Consists in the Consideration of Speculative Sciences?
Objection 1: It would seem that man's happiness consists in the consideration of speculative sciences. For the Philosopher says (Ethic. i, 13) that "happiness is an operation according to perfect virtue." And in distinguishing the virtues, he gives no more than three speculative virtues—"knowledge," "wisdom" and "understanding," which all belong to the consideration of speculative sciences. Therefore man's final happiness consists in the consideration of speculative sciences.
Obj. 2: Further, that which all desire for its own sake, seems to be man's final happiness. Now such is the consideration of speculative sciences; because, as stated in Metaph. i, 1, "all men naturally desire to know"; and, a little farther on (2), it is stated that speculative sciences are sought for their own sakes. Therefore happiness consists in the consideration of speculative sciences.