An effort is necessary in order clearly to perceive what the facts of consciousness are, and what its testimony is; for without this it is impossible to advance one step in the investigation of the first principle of human knowledge. Confusion on this point makes us fall into transcendental equivocations. We shall hereafter have occasion to observe this, and we have already encountered lamentable examples of such deviations in the errors of the philosophy of the _me_.
152. Evidence is usually called an intellectual light. This is a very happy metaphor, and even exact; but, like all metaphors, it has the defect of being of but little service to explain the mysteries of philosophy. We also find intellectual light in many acts of consciousness. There is also a sort of clear light in that intimate presence by which an operation or an impression is offered to the mind; it shines upon the eye of the soul, and makes it see what is before it. If, then, we define evidence only by calling it the light of the intellect, we confound it with consciousness, or, at least, by the use of ambiguous language, give others occasion of confounding them.
Let us not be thought to blame those who have used the metaphor of light, or to flatter ourselves with being able to define evidence with all exactness; for who can express in words this phenomenon of our mind? If we are to have any metaphor, that of the intellectual light seems to be the most adequate. For, in truth, when we fix our attention upon evidence, in order to examine its nature and its effects on the mind, it very naturally presents itself under the image of a light, whose splendor illumines the objects, and enables the mind to contemplate them: but this, we repeat, is not enough. We will, then, although we do not undertake exactly to define it, point out a mark to distinguish it from every thing else.
153. Evidence is always accompanied by the necessity, and consequently, by the universality, of the truths which it attests. There is no evidence of the contingent, except in so far as subjected to a necessary principle.
Let us explain this doctrine by comparing examples taken respectively from consciousness and evidence.
That there is in me a being which thinks, I know, not by evidence, but by consciousness. That whatever thinks exists, I know, not by consciousness, but by evidence. In both cases the certainty is absolute, irresistible; but in the first it rests upon a particular, contingent fact; in the second upon a universal and necessary truth. That I think is certain for me, but not necessarily so for others; the disappearance of my thought does not overturn the world of intelligences; if my thought should now cease to exist, truth in itself would suffer no change; other intellects might and would continue to perceive truth; and neither in the real nor in the ideal order would there be less concert and harmony.