What is human personality? It is a psychic entity whose most important function is to unify the parts of a man's nature. It is the principle of unity and the instrument of unity. A man's thought, will and feeling are distinct and real entities. His intelligence takes various forms from perception to abstract thought; it may be directed to outward things, to thoughts of things, or to pure idea. He wills many things, and wills them in different modes and with varying degrees of intensity. A wide range of feeling is found in him, from physical to mental, from organic to ideal feeling. His nature is tripartite. Each part admits of variation in itself and in its interaction with the other parts. Each of the three expresses the man at the moment. No one of the three gives the whole account of his being. Nor do the three taken together. Though his nature is tripartite the man himself cannot be resolved into component parts. He has his faculties and states, but he is more than their sum. He may lose himself in thought or activity, or abandon himself to feeling, but when he is fulfilling his true function, when he is most himself, all parts of his nature are concentrated to a point. Partial activity of thought, will, or feeling is then replaced by activity of the personality. Personality is the synthetic unity of all parts of a man's nature. It has the wonderful power of compressing to a point a medley of psychic elements. Moods and memories, perceptions and ideas, wishes and purposes, it tensions them all up, merges them and expresses them in characteristic acts representative of the man. Personality differs from nature also in respect of relation to environment. It is relatively independent of circumstances. Habit and education mould the nature, but if they touch the person they do so only indirectly. The nature must be deeply affected before a change in the person is registered. Personality is not synonomous with inherited disposition; but it bears a similar relation to nature as inherited disposition does to acquired habit. It is to nature what character is to action. It is to nature what in Weismann's theory the germ plasm is to the somatic cell. Changes in it are mediated by nature and are almost imperceptible in a life time.