1 It is manifest that there is nothing which men have ever said which is not liable to opposition. Where the will dissents the mind also dissents: under the bias of opposing judgment it joins battle, and denies the assertions to which it objects. Though every word we say be incontrovertible if gauged by the standard of truth, yet so long as men think or feel differently, the truth is always exposed to the cavils of opponents, because they attack, under the delusion of error or prejudice, the truth they misunderstand or dislike.
For decisions once formed cling with excessive obstinacy: and the passion of controversy cannot be driven from the course it has taken, when the will is not subject to the reason. Enquiry after truth gives way to the search for proofs of what we wish to believe; desire is paramount over truth. Then the theories we concoct build themselves on names rather than things: the logic of truth gives place to the logic of prejudice: a logic which the will adjusts to defend its fancies, not one which stimulates the will through the understanding of truth by the reason.
From these defects of partisan spirit arise all controversies between opposing theories. Then follows an obstinate battle between truth asserting itself, and prejudice defending itself: truth maintains its ground and prejudice resists. But if desire had not forestalled reason: if the understanding of the truth had moved us to desire what was true: instead of trying to set up our desires as doctrines, we should let our doctrines dictate our desires; there would be no contradiction of the truth, for every one would begin by desiring what was true, not by defending the truth of that which he desired.
Source: On the Trinity (New Advent)