Objection 1. It seems that good is logically prior to the true. For what is more universal is logically prior, as is evident from Phys. i. But the good is more universal than the true, since the true is a kind of good, namely, of the intellect. Therefore the good is logically prior to the true.
Objection 2. Further, good is in things, but the true in the intellect composing and dividing as said above (Article 2). But that which is in things is prior to that which is in the intellect. Therefore good is logically prior to the true.
Objection 3. Further, truth is a species of virtue, as is clear from Ethic. iv. But virtue is included under good; since, as Augustine says (De Lib. Arbit. ii, 19), it is a good quality of the mind. Therefore the good is prior to the true.
On the contrary, What is in more things is prior logically. But the true is in some things wherein good is not, as, for instance, in mathematics. Therefore the true is prior to good.
I answer that, Although the good and the true are convertible with being, as to suppositum, yet they differ logically. And in this manner the true, speaking absolutely, is prior to good, as appears from two reasons.
First, because the true is more closely related to being than is good. For the true regards being itself simply and immediately; while the nature of good follows being in so far as being is in some way perfect; for thus it is desirable.
Secondly, it is evident from the fact that knowledge naturally precedes appetite. Hence, since the true regards knowledge, but the good regards the appetite, the true must be prior in idea to the good.
Reply to Objection 1. The will and the intellect mutually include one another: for the intellect understands the will, and the will wills the intellect to understand. So then, among things directed to the object of the will, are comprised also those that belong to the intellect; and conversely. Whence in the order of things desirable, good stands as the universal, and the true as the particular; whereas in the order of intelligible things the converse of the case. From the fact, then, that the true is a kind of good, it follows that the good is prior in the order of things desirable; but not that it is prior absolutely.
Reply to Objection 2. A thing is prior logically in so far as it is prior to the intellect. Now the intellect apprehends primarily being itself; secondly, it apprehends that it understands being; and thirdly, it apprehends that it desires being. Hence the idea of being is first, that of truth second, and the idea of good third, though good is in things.
Reply to Objection 3. The virtue which is called "truth" is not truth in general, but a certain kind of truth according to which man shows himself in deed and word as he really is. But truth as applied to "life" is used in a particular sense, inasmuch as a man fulfills in his life that to which he is ordained by the divine intellect, as it has been said that truth exists in other things (1). Whereas the truth of "justice" is found in man as he fulfills his duty to his neighbor, as ordained by law. Hence we cannot argue from these particular truths to truth in general.
Source: Summa Theologica (New Advent)