The mechanical explanation of phenomena and the determinism of science only become exclusive of teleology when they are transformed into metaphysical materialism--that is to say, when it is affirmed, _a priori_, and by a subjective act, that there is nothing in the universe but matter and the movements of matter. But then, it is clear that materialism, which believes itself to be scientific, becomes a philosophy, and like all other philosophies it falls under the jurisdiction not only of the objective science of the world, but of the consciousness of the ego. The ideas of cause and end spring from one and the same source. The idea of cause awakens in us because the ego, as soon as it knows itself, has the clear sense of being the author of its acts; it has this sense by that of the very effort that it has made. But, at the same time, it knows that it made that effort with a view to an end which attracted it. Cause and end, therefore, are the two aspects of the same conscious act. The one is the backward glance of the consciousness; the other is its forward look. As we only know the world by reflecting it in the mirror of our consciousness, it follows that the two categories of cause and end impose themselves on our understanding with an equal necessity. There is another consequence of this psychological observation. The consciousness of the ego is one; neither the idea of cause nor the idea of end, by itself, would suffice to explain the whole universe to me. It is easy to see at a glance that the objective science of phenomena is not and never can be completed. The chain into which it introduces each particular phenomenon as a new link is indefinitely lengthened by scientific progress, in time and space, but without the power to hang on anywhere. Outside space and time, the principle of causation only engenders insoluble antinomies. Besides, to explain one phenomenon by another is to explain it by a cause which itself needs explanation. The mechanical reason of things is therefore never a sufficient reason. It is an indefinite series of insufficient particular reasons. The network of science, however fine and firm it be, does not cover, and cannot cover all reality. The Cosmos that science builds is like the globe; it floats in immensity. "Where, O Lord, goes the earth through the heavens?"