“However, it seems indeed better, and in fact especially obligatory on philosophers, to sacrifice even the rights of friendship for the sake of truth. While it is commendable to have love for both, we ought to honor truth as sacred above friends.” (Aristotle: Nicomachean Ethics, 106a14-17.)
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76) ...."The reason that it seems to be better, meaning more honorable and in agreement with good morals, and indeed obligatory, that a man should not hesitate to oppose his friends for the sake of truth. It is so necessary for good morals that without it virtue cannot be preserved. Unless a man prefer truth to his friends, it follows that he will make false judgment and bear false witness in their defense. This is contrary to virtue. While reason prescribes that all men should prefer truth to their friends, this holds in a special way for the philosophers whose calling is to study wisdom, which is knowledge of the truth.
77) “That truth should be preferred to friends he proves in this way. He is the greater friend for whom we ought to have the greater consideration. Although we should have friendship for both truth and our fellow man, we ought rather to love truth because we should love our fellow man especially on account of truth and virtue, as will be shown in the eighth book. Now truth is a most excellent friend of the sort to whom the homage of honor is due. Besides, truth is a divine thing, for it is found first and chiefly in God. He concludes, therefore that it is virtuous to honor truth above friends.
78) “Andronicus, the peripatetic, says that piety makes men faithful to and observant of the things of God. Along the same line is the judgment of Plato who, in rejecting the opinion of his teacher Socrates, says a man ought to care more for the truth than anything else. Somewhere else too he affirms that while Socrates is certainly his friend, truth is still more so. In yet another place he says that we should have some care for the views of Socrates but more for the truth.”
~St. Thomas Aquinas: Commentary on Aristotle’s Nicomachean Ethics, Bk. I, Lect. VI.