In this case the practical end in view can be but one. We know in order to act; and he who acts is interested only in that knowledge, which is the necessary precedent of his doing. But since our knowledge is all destined to be recalled as occasion serves for action, or to aid us in the search for new knowledge (which in this case is a form of acting), the practical spirit is impelled to provide for the preservation of the patrimony of acquired knowledge. Without doubt, speaking absolutely, everything is preserved in reality, and nothing that has once been done or thought, disappears from the bosom of the cosmos. But the preservation of which we speak, is properly the making easily available to memory, knowledge that has once been possessed, and providing for its ready recall from the bosom of the cosmos or from the apparently unconscious and forgotten. For this purpose there are constructed those instruments, which are conceptual fictions, by means of which armies of representations are evoked with a single word, or by which a single word approximately indicates what form of operation must be resorted to, in order that certain representations may be recovered. The cat of the appropriate conceptual fiction does not enable us to know any single cat, as a painter or a historian of cats makes us know it; but by means of it, many images of animals, which would have remained separate before the memory, or each one dispersed and fused in the complete picture in which it had been imagined and perceived, are arranged in a series and recorded as a whole. This matters little or nothing to one who dreams as a poet or who seeks absolute truth; but it matters a great deal to one whose house is infested by rats, and who must employ some one to obtain a cat; and it matters not less to the seeker for the cat, in that he has to study a new animal, and that he must proceed in that study with some order, though it be artificial, and though he reject the artifice in the final synthesis. Again, the geometrical triangle is of no service either to imagination or to thought, which are developed without it; but it is indispensable to any one measuring a field, in the same way as it may possibly be of service to a painter in his preparatory studies for a picture, or to a historian, who wishes to know well the configuration of a piece of ground where a battle was fought. [Sidenote: _Persistence of conceptual fictions side by side with concepts._]