With them, nearly every source of belief is suspicious.

At bottom, among the ways of acquiring knowledge, they accept but two, the most direct, the simplest, the best tested, and again on condition that one proves the other, the type of the first being that process of reasoning by which we show that two and two make four, and the second that experience by which we demonstrate that heat above a certain degree melts ice, and that cold below a certain degree freezes water.

This is the sole process that is convincing; all others, less and less sure in proportion as they diverge from it, possess only a secondary, provisional and contestable value, that which it confers on them after verification and check .-- Let us accordingly avail ourselves of this one, and not of another, to express, restrain or suspend our judgment.

So long as the intellect uses it and only it, or its analogues, to affirm, set aside or doubt, it is called reason, and the truths thus obtained are definitive acquisitions.

Acquired one by one, the truths thus obtained have for a long time remained scattered, in the shape of fragments; only isolated sciences have existed or bits of science.