about between its existence and its appearance. No doubt it has become difficult to avoid this dissociation now that philosophers have made it. To forget it, however, is what we ask of the reader. If, in the course of this first chapter, objections arise in his mind against any of the views that we put forward, let him ask himself whether these objections do not imply his return to one or the other of the two points of view above which we urge him to rise.
Philosophy made a great step forward on the day when Berkeley proved, as against the 'mechanical philosophers,' that the secondary qualities of matter have at least as much reality as the primary qualities. His mistake lay in believing that, for this, it was necessary to place matter within the mind, and make it into a pure idea. Descartes, no doubt, had put matter too far from us when he made it one with geometrical extensity. But, in order to bring it nearer to us, there was no need to go to the point of making it one with our own mind. Because he did go as far as this, Berkeley was unable to account for the success of physics, and, whereas Descartes had set up the mathematical relations between phenomena as their very essence, he was obliged to regard the mathematical order of the universe as a mere accident. So the Kantian criticism became necessary, to show the reason of this mathematical order and to give back to our physics a solid foundation—a task in which, however, it succeeded
