"The popular notion is that a true idea must copy its reality. Like other popular views, this one follows the analogy of the most usual experience. Our true ideas of sensible things do indeed copy them. Shut your eyes and think of yonder clock on the wall, and you get just such a true picture or copy of its dial. But your idea of its 'works' (unless you are a clockmaker) is much less of a copy, yet it passes muster, for it in no way clashes with reality. Even though it should shrink to the mere word 'works', that word still serves you truly; and when you speak of the 'time-keeping function' of the clock, or of its spring's 'elasticity', it is hard to see exactly what your ideas can copy."