Reasoning is compared to understanding as movement is to rest, or acquisition to possession.... Since movement always proceeds from something immovable, and ends in something at rest, hence it is that human reasoning, in the order of inquiry and discovery, proceeds from certain things absolutely understood--namely, the first principles; and, again, in the order of judgment, returns by analysis to first principles, in the light of which it examines what it has found. Now it is clear that rest and movement are not to be referred to different powers, but to one and the same.
Thomas AquinasThe last end of every maker, as such, is himself, for what we make we use for our own sake; and if at any time a man make a thing for the sake of something else, it is referred to his own good, whether his use, his pleasure, or his virtue.
Thomas AquinasSince faith rests upon infallible truth, and since the contrary of a truth can never be demonstrated, it is clear that the arguments brought against faith cannot be demonstrations, but are difficulties that can be answered.
Thomas Aquinas