Objection 1. It would seem that honesty is not the same as virtue. For Tully says (De Invent. Rhet. ii, 53) that "the honest is what is desired for its own sake." Now virtue is desired, not for its own sake, but for the sake of happiness, for the Philosopher says (Ethic. i, 9) that "happiness is the reward and the end of virtue." Therefore honesty is not the same as virtue.
Objection 2. Further, according to Isidore (Etym. x) "honesty means an honorable state." Now honor is due to many things besides virtue, since "it is praise that is the proper due of virtue" (Ethic. i, 12). Therefore honesty is not the same as virtue.
Objection 3. Further, the "principal part of virtue is the interior choice," as the Philosopher says (Ethic. viii, 13). But honesty seems to pertain rather to exterior conduct, according to 1 Corinthians 14:40, "Let all things be done decently [honeste] and according to order" among you. Therefore honesty is not the same as virtue.
Objection 4. Further, honesty apparently consists in external wealth. According to Sirach 11:14, "good things and evil, life and death [poverty and riches] are from God" [The words in brackets are omitted in the Leonine edition. For riches the Vulgate has 'honestas']. But virtue does not consist in external wealth. Therefore honesty is not the same as virtue.
On the contrary, Tully (De Offic. i, 5; Rhet. ii, 53) divides honesty into the four principal virtues, into which virtue is also divided. Therefore honesty is the same as virtue.
I answer that, As Isidore says (Etym. x) "honesty means an honorable state," wherefore a thing may be said to be honest through being worthy of honor. Now honor, as stated above (144, 2, ad 2), is due to excellence: and the excellence of a man is gauged chiefly according to his virtue, as stated in Phys. vii, 17. Therefore, properly speaking, honesty refers to the same thing as virtue.
Reply to Objection 1. According to the Philosopher (Ethic. i, 7), of those things that are desired for their own sake, some are desired for their own sake alone, and never for the sake of something else, such as happiness which is the last end; while some are desired, not only for their own sake, inasmuch as they have an aspect of goodness in themselves, even if no further good accrued to us through them, but also for the sake of something else, inasmuch as they are conducive to some more perfect good. It is thus that the virtues are desirable for their own sake: wherefore Tully says (De Invent. Rhet. ii, 52) that "some things allure us by their own force, and attract us by their own worth, such as virtue, truth, knowledge." And this suffices to give a thing the character of honest.
Reply to Objection 2. Some of the things which are honored besides virtue are more excellent than virtue, namely God and happiness, and such like things are not so well known to us by experience as virtue which we practice day by day. Hence virtue has a greater claim to the name of honesty. Other things which are beneath virtue are honored, in so far as they are a help to the practice of virtue, such as rank, power, and riches [Ethic. i, 8. For as the Philosopher says (Ethic. iv, 3) that these things "are honored by some people, but in truth it is only the good man who is worthy of honor." Now a man is good in respect of virtue. Wherefore praise is due to virtue in so far as the latter is desirable for the sake of something else, while honor is due to virtue for its own sake: and it is thus that virtue has the character of honesty.
Reply to Objection 3. As we have stated honest denotes that to which honor is due. Now honor is an attestation to someone's excellence, as stated above (103, 1 and 2). But one attests only to what one knows; and the internal choice is not made known save by external actions. Wherefore external conduct has the character of honesty, in so far as it reflects internal rectitude. For this reason honesty consists radically in the internal choice, but its expression lies in the external conduct.
Reply to Objection 4. It is because the excellence of wealth is commonly regarded as making a man deserving of honor, that sometimes the name of honesty is given to external prosperity.
Source: Summa Theologica (New Advent)