CHAPTER V.
The fifth chapter commences with an examination of the distinction between man and the brutes. Man possesses reason, that is to say, he has a class of ideas of which the brutes are not capable, abstract ideas as distinguished from those ideas of perception from which the former kind are yet derived. The consequence is, that the brute neither speaks nor laughs, and lacks all those qualities which make human life great. The nature of motives, too, is different where abstract ideas are possible. No doubt the actions of men follow of necessity from their causes, not less than is the case with the brutes, but the kind of sequence through thought which renders choice, i.e., the conscious conflict of motives, possible is different. Our abstract ideas, being incapable of being objects of perception, would be outside consciousness, and the operations of thought would be impossible, were it not that they are fixed for sense by arbitrary signs called words, which therefore always indicate general conceptions. It is just because the brutes are incapable of general conceptions that they have no faculty of speech. But thought does not consist in the mere presence of abstract ideas in consciousness, but in the union and separation of two or more of them, subject to the manifold restrictions and modifications which logic deals with. Such a clearly expressed conceptual relation is a judgment. In relation to judgments the principle of sufficient reason is valid in a new form: that of the ground of knowing. In this form it asserts that if a judgment is to express knowledge it must have a ground; and it is just because it has a ground that it has ascribed to it the predicate true. The grounds on which a judgment may depend are divisible into four kinds. A judgment may have another judgment as its ground, in which case its truth is formal or logical. There is no truth except in the relation of a judgment to something outside it, and intrinsic truth, which is sometimes distinguished from extrinsic logical truth, is therefore an absurdity. A judgment may also have its ground in sense-perception, and its truth is then material truth. Again, those forms of knowledge which
