so on. It does no special practical good to discuss instincts as if they operated in man as such. They become purposes. Therefore we shall defer the consideration of instincts and purposes in detail until later chapters of this book. Since instincts are too rigid to meet the needs of the social and traditional life of man, they become intellectualized and socialized into purposes and ambitions, sometimes almost beyond recognition. Nevertheless, the driving force of instinct is behind every purpose, every ambition, even though the individual himself has not the slightest idea of the force that is at work. This does not mean that instinct acts as a sort of cellar- plotter, roving around in a subconsciousness, or at least no such semi-diabolical personality need be postulated, any more than it need be postulated for the automatic mechanism that regulates heartbeat or digestion. The organic tensions and depressions that constitute instinct are not conscious or subconscious; they affect our conscious personalities so that we desire something, we fit that desire in with the rest of our desires, we seek the means of gratifying that desire first in accordance with means that Nature has given us and second in accordance with social teaching and our intelligence. If the desire brings us sharply in contact with obstacles imposed either by circumstances or more precious desire, we inhibit that desire,--and thus the instinct. Because organic tensions and depressions are periodic and are dependent upon the activities of glands and tissues not within our control, the desires may never be completely squelched and may arise as often as some outer stimulus brings them into activity, to plague and disorder the life of the conscious personality. 3. With this preliminary consideration of instinct, we pass on to certain of the phases of intelligence. How to define intelligence is a difficulty best met by ignoring definition. But this much is true: that the prime function of intelligence is to store up the past and present experiences so that they can be used in the future, and that it adds to the rigid mechanism of instinct a plastic force which by inhibiting and exciting activity according to need steers the organism through intricate channels.