_Existence of first Truths._--All science and all reasoning depend ultimately on certain first truths or principles, not learned by experience, but prior to it, the evidence and certainty of which lie back of all reasoning and all experience. Take away these elementary truths, and neither science nor reasoning are longer possible, for want of a beginning and foundation. Every proposition which carries evidence with it, either contains that evidence in itself, or derives it from some other proposition on which it depends. And the same is true of this other proposition, and so on forever, until we come, at last, to some proposition which depends on no other, but is self-evident, a first truth or principle. Whence come these first principles? Not of course from experience, for they are involved in and essential to all experience. They are native or _à priori_ convictions of the mind, instinctive and intuitive judgments. _Existence of first Truths admitted._--The existence of first truths or principles, as the basis of all acquired knowledge, has been very generally admitted by philosophers. They have designated these elementary principles, however, by widely different appellations. By some, they have been termed _instinctive_ beliefs, cognitions, judgments, etc., an appellation mentioned by Hamilton as employed by a very great number of writers from Cicero downward, including, among the rest, Scaliger, Bacon, Descartes, Pascal, Leibnitz, Hume, Reid, Stewart, Jacobi. Others, again, have termed them _à priori_ or _transcendental_ principles, cognitions, judgments, etc., as being prior to experience, and transcending the knowledge derived from sense. So Kant and his school termed them. By the Scotch writers they have been termed, also, principles of _common sense_, in place of which expression Stewart prefers the title, _fundamental laws of human belief_.