PROOF is of three kinds: First, the Logical, which rests on premises, and demonstrates that according to the laws of the human mind a certain conclusion follows.

2nd. The Historical, which shows that if the case be as affirmed, the course of human thought in relation to it must have been such as it has been. It accounts for the rise and progress of opinion.

3rd. That which might be called the Expository, which, taking the phenomena as they appear, gives a simple statement of the fact which carries its own conviction. Such is the evidence on which the Copernican astronomy is received by the mass of educated men.

Each of these modes of proof is indispensable; but they are by no means of equal authority. The logical is principally useful as a means for advancing knowledge. Its conclusions can never have more certainty than the premises, and its end is chiefly to free us from false ideas by leading us to false results when we reason from them. It makes the latent error manifest. Logic has less to do with that which is true than with that which it is reasonable for us to think with our particular amount of knowledge. The historical and expository proof have more positive value. The light which they throw upon that which has been, and which is, gives them an authority to a certain degree independent of ourselves.

The argument from premises to conclusions will be the least employed here, not because it is inapplicable, but because it is the least appropriate. It neither can nor should produce conviction.