tendency or groping impulse, not to any exact law. No, we must say instead: _In the universe at large_ the whole past is preserved bodily in the present; duration is real and space is only imagined; all is motion, and there is nothing substantial that moves; times are incommensurable; men, birds, and waves are nothing but the images of them (our perceptions, like their spirits, being some compendium of these images); chance intervenes in the flux, but evolution is due to an absolute Effort which exists _in vacuo_ and is simplicity itself; and this Effort, without having an idea of what it pursues, nevertheless produces it out of nothing. The accuracy or the hollowness of M. Bergson's doctrine, according as we take it for literary psychology or for natural philosophy, will appear clearly in the following instance. "Any one," he writes,[3] "who has ever practised literary composition knows very well that, after he has devoted long study to the subject, collected all the documents, and taken all his notes, one thing more is needful before he can actually embark on the work of composition; namely, an effort, often a very painful one, to plant himself all at once in the very heart of the subject, and to fetch from as profound a depth as possible the momentum by which he need simply let himself be borne along in the sequel. This momentum, as soon as it is acquired, carries the mind forward along a path where it recovers all the facts it had gathered together, and a thousand other details besides. The momentum develops and breaks up of itself into particulars that might be retailed _ad infinitum._ The more he advances the more he finds; he will never have exhausted the subject; and nevertheless if he turns round suddenly to face the momentum he feels at his back and see what it is, it eludes him; for it is not a thing but a direction of movement, and though capable of being extended indefinitely, it is simplicity itself." [Footnote 3: "Introduction a la Metaphysique." _Revue de Metaphysique et de Morale_, Janvier, 1903.]