Thus understood, the relation of causality is a necessary relation in the sense that it will indefinitely approach the relation of identity, as a curve approaches its asymptote. The Principle of identity is the absolute law of our consciousness: it asserts that what is thought is thought at the moment when we think it: and what gives this principle its absolute necessity is that it does not bind the future to the present, but only the present to the present: it expresses the unshakable confidence that consciousness feels in itself, so long as, faithful to its duty, it confines itself to declaring the apparent present state of the mind. But the principle of causality, in so far as it is supposed to bind the future to the present, could never take the form of a necessary principle; for the successive moments of real time are not bound up with one another, and no effort of logic will succeed in proving that what has been will be or will continue to be, that the same antecedents will always give rise to identical consequents. Descartes understood this so well that he attributed the regularity of the physical world and the continuation of the same effects to the constantly renewed grace of Providence; he built up, as it were, an instantaneous physics, intended for a universe the whole duration of which might as well be confined to the present moment. And Spinoza maintained that the indefinite series of phenomena, which takes for us the form of a succession in time, was equivalent, in the absolute, to the divine unity: he thus assumed, on the one hand, that the relation of apparent causality between phenomena melted away into a relation of identity in the absolute, and, on the other, that the indefinite duration of things was all contained in a single moment, which is eternity. In short, whether we study Cartesian physics, Spinozistic metaphysics, or the scientific theories of our own time, we shall find everywhere the same anxiety to establish a relation of logical necessity between cause and effect, and we shall see that this anxiety shows itself in a tendency to transform relations of succession into relations of inherence, to do away with active duration, and to substitute for apparent causality a fundamental identity. [Sidenote: The necessary determination of phenomena implies non-duration; but we _endure_ and are therefore free.]