The materials in the present chapter are intended to illustrate the fact that individuality of the person and of the group is both an effect of and a cause of isolation. The first selections under the heading "Isolation and Personal Individuality" bring out the point that the function of isolation in personal development lies not so much in sheer physical separation from other persons as in freedom from the control of external social contacts. Thus Rousseau constructs an ideal society in the solitude of his forest retreat. The lonely child enjoys the companionship of his imaginary comrade. George Eliot aspires to join the choir invisible. The mystic seeks communion with divinity. This form of isolation within the realm of social contacts is known as privacy. Indeed privacy may be defined as withdrawal from the group, with, at the same time, ready access to it. It is in solitude that the creative mind organizes the materials appropriated from the group in order to make novel and fruitful innovations. Privacy affords opportunity for the individual to reflect, to anticipate, to recast, and to originate. Practical recognition of the human demand for privacy has been realized in the study of the minister, the office of the business man, and the den of the boy. Monasteries and universities are institutions providing leisure and withdrawal from the world as the basis for personal development and preparation for life's work. Other values of privacy are related to the growth of self-consciousness, self-respect, and personal ideals of conduct. Many forms of isolation, unlike privacy, prevent access to stimulating social contact. Selections under the heading "Isolation and Retardation" indicate conditions responsible for the arrest of mental and personal growth. The cases of feral men, in the absence of contradictory evidence, seem adequate in support of Aristotle's point that social contacts are indispensable for human development. The story by Helen Keller, the talented and celebrated blind deaf-mute, of her emergence from the imprisonment of sense deprivation into the free life of communication is a most significant sociological document. With all of us the change from the animal-like isolation of the child at birth to personal participation in the fullest human life is gradual. In Helen Keller's case the transformation of months was telescoped into minutes. The "miracle" of communication when sociologically analyzed seems to consist in the transition from the experience of _sensations_ and _sense perceptions_ which man shares in common with animals to the development of _ideas_ and _self-consciousness_ which are the unique attributes of human beings.