96. However vague the ideas an isolated being would form of objects distinct from itself, they will never be so vague as not to refer to a real thing. The mind may not know the nature of this reality, but it knows for certain that it exists. A man blind from his birth can form no clear idea of colors, nor of the sensation of seeing; but is he therefore ignorant that sensation exists, and that the words, color, seeing, and others which refer to sight, have a positive and determinate object? Certainly not. The blind man does not know in what these things, of which he hears, consist, but he knows that they are something; those of his conceptions that refer to them may be called imperfect, but they are not vain; the words by which he expresses them, have for him a positive, although incomplete meaning. 97. There is a great difference between incomplete and indeterminate conceptions; the former may refer to a positive thing, although imperfectly known; the latter include nothing but a relation of ideas, meaning nothing in the order of facts. We will render this difference more apparent by explaining the example of the preceding paragraph. A man blind from his birth has no intuition of colors, nor of any thing that refers to the sense of sight; but he is sure that there exist external facts which correspond to an internal affection called _seeing_. This idea is incomplete, but it has a determinate object. The words of those who possess the sense of sight reveal to him its existence; he knows not, what it is, but, that it is; in other words, he does not know its essence, but its existence. Let us now suppose the possibility of an order of sensations different from ours, and in nowise resembling those which we experience, to be called in question. The conception referred to the new sensations would not only be incomplete, but would have no relation to any real object. The general idea, then, of affection of a sensitive being, will be all that our mind will have; but it will know nothing of its existence, and can form only mere conjectures as to the conditions of its possibility. This example illustrates our idea. We find in the man blind from his birth, who hears of what pertains to the sense of sight, an incomplete conception, but one to which the existence of a series of facts, known to his mind, corresponds. But in ourselves, if we reflect upon a kind of sensations different from our own, we find conceptions, having, indeed, a general object, but of whose realization we know nothing. 98. Thus is it explained how our mind, without having intuition of a thing, can, nevertheless, know it, and be perfectly certain of its existence. We have here demonstrated that conceptions may, although they do not refer to a sensible intuition, have a value, not only in the order of ideas, but also in that of facts.