THE TRUTH OF FIRST PRINCIPLES.
1. You ask “my idea on the impossibility of proving the truth of First Principles?”
By “truth” you mean the ascertained existence of any idea or thing, and the ascertained consistency of any statement with some such idea or thing.
By “principles” you mean not simply cardinal propositions, but cardinal propositions that we have ascertained to be true.
By “first principles” you mean the indubitably true but unprovable elementary principles of all our knowledge. You mean that these principles are the ground whereon we build in our reasonings; all that we build upon them must, in consequence of being so built, admit of being “proved” whether we have built rightly—that is, admit of being subjected to the test whether the reasoning is correct; but these “first principles” are confessedly exempted from this test, and yet are received as true, no less than the others that have sustained this ordeal. You ask the meaning of this privilege, whether it is right; and, if so, to what propriety or necessity of the case it is due?
2. You ask, “How is truth ascertained to be truth?” or, in other words, “What is the criterion of truth?”
With respect to the first query—In accordance with the definition I have above given of truth, it would seem that it must have two sources, experience and reason, experience who notifies the existence of certain ideas or things, and reason, who forms propositions suggested by them. Experience, therefore, acts the simple part of supplying all the materials of truth; while reason, besides his acknowledged office of judge of all truth, exercises the quite different function of being himself the purveyor of a portion of it.
So indubitable is it that truth can have these two sources only, that even fanaticism would be found confessing the principle; while it appeals to the experience of those who agree with it, as well as professes to be reasonable.
First principles must, accordingly, be of two kinds. Of those that are based upon experience, I will give the following instances:—I hear the chirping of a bird, and I see an inkstand before me. That I have the sensation of hearing and seeing in these two cases, are facts of which it is impossible I can doubt. Reason perceives that these are primary facts or first principles, neither admitting nor requiring any proof, testified by consciousness, and self-evidently verified on that testimony.
By reason, of course is meant the reason of all mankind—that is, of all who are presumably competent to judge on the subject. So that any just or reasonable confidence in the verdict of my own reason—in this or in any other matter, presupposes a due comparison of my own reason with that of others, nay, in some cases, a consideration of the supposably more enlightened reason of future times.