To understand the way in which the intellect serves the living creature endowed with it, we need only regard it from the standpoint of ordinary experience. We know in ourselves that our life is wider than our intellect, and that our intellect serves the activity of our life. The common expressions we employ, such as using our wits, taking an intelligent interest, trying to think, all imply a utility distinct from the intellect. So viewed, our life appears as an active principle within us, maintaining our organism in its relations, active and passive, and reactive to the reality outside and independent of it. Our intellect also seems both active and passive. It receives the influences that stream in upon us from the reality around us, it apprehends and interprets them, and works out the lines of our possible action in regard to them. The influences that flow in upon us from the outside world are already selected before our intellect apprehends them, for they flow in by the avenues of our senses, and the senses are natural instruments of selection. If we picture these influences as vibrations, then we may say that a certain group of vibrations of a very rapid frequency are selected by the eye and give rise to vision, that another group of very much lower frequency are selected by the ear and { 65} give the sensation of sound, and other groups are selected by taste, smell, and touch. Many groups are known indirectly by means of artificial instruments, and all the infinite series that unite these groups of the actually experienced vibrations escape our apprehension altogether--we have no means of selecting them. But all these sense data, as we may call them, come to us without exertion or activity on our part; it is the intellect which gives them meaning, which interprets them, which makes them the apprehension or awareness of objects or things. And the active part that the intellect plays is also a process of selection. This is evident if we reflect upon the universal form which our intellectual activity takes, namely, attention. It is in the act of attention that we are conscious of mental activity, and attention is essentially selection--the selection of an interest. Besides the natural selection that is effected by our senses and the conscious selection that is manifest in attention, there is also a more or less arbitrary selection that our intellect performs in marking out the lines of our practical interest and possible action. In this work of selection the intellect makes the world conform to the necessities of our action.