CHAPTER XXIV.

      THE CRITERION OF EVIDENCE.

       Table of Contents

      239. There are two species of evidence, mediate and immediate. We call immediate evidence that which requires only understanding of the terms; and mediate evidence that which requires reasoning. That the whole is greater than its part is evident by immediate evidence; that the square of the hypothenuse is equal to the sum of the squares of the other two sides, is known by mediate evidence, that is, by demonstrative reasoning.

      240. We have said that one of the distinctive characteristics of evidence is the necessity and universality of its object. This is a characteristic as well of mediate as of immediate evidence.

      Besides this characteristic there is another, called with more reason essential, notwithstanding some doubt as to whether it extends to mediate evidence or not; it is that the idea of the predicate is found contained in that of the subject. This is the most complete essential notion of the criterion of immediate evidence, by which it is distinguished from the criteria of consciousness and common sense.

      We have said there is some doubt as to this characteristic extending to mediate evidence; by this we mean that also in mediate evidence the idea of the predicate may be contained in that of the subject. In this it is not our intention to ignore the difference between theorems and axioms, but to call the reader's attention to a doctrine which we propose to develop, while treating of mediate evidence. In the present chapter we shall only treat of evidence in general, or of immediate evidence alone.

      241. Evidence involves relation, for it implies comparison. When the understanding does not compare, it has no evidence, but only a perception, which is a pure fact of consciousness; and this evidence does not refer to perception alone, but always supposes or produces a judgment.

      We find two things in every act where there is evidence: the pure intuition of the idea, and the decomposition of this idea into various conceptions accompanied with the perception of their mutual relations. This we will explain by an example from geometry. The triangle has three sides: this is an evident proposition, for in the very idea of triangle, we find the three sides; and in conceiving the triangle, we in some sense conceive the three sides. Had we limited ourselves to the contemplation of the simple idea of triangle, we should have had intuition of the idea, but not evidence, which begins only when we find, in decomposing the conception of triangle, and considering in it the idea of figure in general, of side, and of the number three, these all contained in the primitive conception. Evidence consists in the clear conception of this.

      So true is this that the very nature of things makes common language philosophical. We do not say, an idea is evident, but a judgment is: no one calls a term evident, but a proposition only. And why? Because the term simply expresses the idea without any relation, or decomposition into its partial conceptions; whereas the proposition expresses the judgment, that is, affirms or denies that one conception is contained in another, which, in the present matter, supposes decomposition of the entire conception.

      242. Immediate evidence is the perception of identity between various conceptions, separated by the analytical power of the intellect. Thus identity combined in a certain way with diversity is not a contradiction, as it might at first sight seem, but something very natural, if we observe one of the most constant facts of our intellect, the faculty of analyzing the most simple conceptions, and of seeing relations between identical things.

      What are all axioms? What are all propositions per se notæ? Nothing but expressions, in which it is affirmed that a predicate belongs to the essence of the subject, or is contained in its idea. The mere conception of the subject includes the predicate: the term which denotes the first also denotes the second; yet the intellect, with a mysterious power of analysis, distinguishes between identical things, and then compares them in order to make them again identical. Whoever says triangle, expresses a figure composed of three sides and three angles; but the intellect may take this idea and consider in it the ideas of the number three, side, and angle, and compare them with the primitive conception. In this distinction there is no deception; there is only the exercise of the faculty, which regards the thing under different aspects, in order to arrive at the intuition and affirmation of the identity of the very things it had before distinguished.

      243. Evidence is a sort of calculation of the intellect, whereby it finds in the conception analyzed whatever was placed in the principle or was contained in it. Hence the necessity and universality of the object of evidence, inasmuch as, and in the manner, in which it is expressed by the idea. To this there are no exceptions. Either a predicate is or is not placed in a primitive principle: if it is, it is there, according to the principle of contradiction. Either it was or was not excluded from the conception; if the conception itself excludes or denies it, this it does by virtue of the principle of contradiction.

      Thus the more fundamental of the two characteristics of evidence given above is, that the idea of the predicate is contained in the idea of the subject. Hence the necessity and universality; since, in verifying this condition, it is impossible for the predicate not to belong necessarily to all the subjects.

      244. Thus far we have encountered no difficulty, because we have treated only of evidence subjectively considered, that is, as relating to pure conceptions; but the intellect does not stop with the conception, but extends to the object, and says not only that it sees the thing, but that the thing is as it sees it. Thus the principle of contradiction, considered in the purely subjective