It is thus that we know the world; which is tantamount to stating that the world exists, so far as we are concerned, only so long as we think so. Reason would go further: it would seize the most general, the universal, beyond experience, beyond the limited and restricted systematizations established by the understanding; to know, for instance, the first cause of all causes, the last and collective end, so to speak, of all purposes; to know "why is there something?" and "in view of what end is there something?" in fact, to answer all the questions of infinity and eternity. Be sure that it cannot. How could it? It only operates, can only operate, on the data of experience and the systematizations of the understanding, which classify experience but do not go beyond it. Only operating upon that, having nothing except that as matter, how could it itself go beyond experience? It cannot. It is only (a highly important fact, and one which must on no account be forgotten)--it is only a sign, merely a witness. It is the sign that the human spirit has need of the absolute; it is itself that need; without that it would not exist; it is the witness of our invincible insistence on knowing and of our tendency to estimate that we know nothing if we only know something; it is itself that insistence and that tendency: without that it would not exist. Let us pause there for the moment. Man knows of nature only those impressions which he receives from it, co-ordinated by the forms of sensibility, and further the ideas of it which he preserves co-ordinated by the forms of his understanding. This is very little. It is all, if we consider only pure reason.