The art of persuasion has a necessary relation to the manner in which men are led to consent to that which is proposed to them, and to the conditions of things which it is sought to make them believe.

No one is ignorant that there are two avenues by which opinions are received into the soul, which are its two principal powers: the understanding and the will. The more natural is that of the understanding, for we should never consent to any but demonstrated truths; but the more common, though the one contrary to nature, is that of the will; for all men are almost led to believe not of proof, but by attraction. This way is base, ignoble, and irrelevant: every one therefore disavows it. Each one professes to believe and even to love nothing but what he knows to be worthy of belief and love.