At a certain stage in his development the caterpillar builds himself a cocoon. His dwelling is a wonderful structure, but from our human point of view the remarkable thing is that he does not learn to build it. He may never have seen a cocoon before, and he constructs only one in his life. Yet his work is perfect, or at least very excellent, and it is as good in its beginnings as in its endings. Evidently he owes nothing to experience, but is impelled and guided throughout by a faculty which we term _instinct_. An instinct may be defined as an innate, inherited impulse, an inclination to do a certain definite act, the instinctive act, on receipt of a certain definite stimulus or incitement to action. In the case of the caterpillar the stimulus appears to be the sight at the proper time of a suitable spot in which to build a cocoon. Since this particular impulse does not appear at the beginning of conscious life, it is termed a deferred instinct. Man, on the other hand, cannot build his house unless he first learns how to build. He depends, not on instinct, but on experience. The faculty by means of which experience is stored in the mind is _memory_. The faculty by means of which we use stored experience to guide present or future conduct is _intelligence_. When the contents of memory are very vast, and the processes of thought by which they are utilised comparatively difficult and complex, intelligence is termed _reason_. Intelligence and reason depend, therefore, on memory, on ability to learn, on capacity to profit by experience. Memory is not the whole of intelligence, but it is the basis of it. Without memory there could be feeling and emotion, but no thought, for the materials of thought would be lacking. [Sidenote: Instinct in Place of Memory] [Sidenote: The Basis of Rational Action]