Classification into kinds is the beginning of most sciences-kinds of rocks, kinds of clouds, kinds of plants, and so on. Thus it is not surprising that the first students of human nature tried to classify kinds of people. One of the earliest “personality theories” attempted to classify individuals into personality types on the basis of body build (Kretschmer, 1925; Sheldon, 1954).
A short, plump person (endomorph) was said to be sociable, relaxed, and even tempered; a tall, thin person (ectomorph) was characterized as restrained, self-conscious, and fond of solitude; a heavy-set, muscular individual (mesomorph) was described as noisy, callous, and fond of physical activity. Although a person’s physique may well have some influence on personality, the relationship is much more subtle than this sort of classification implies, and research has shown little correlation between body build and specific personality characteristics (Tyler, 1956).
Personality type theories have also been based on purely psychological characteristics. One of Freud’s pupils, the Swiss psychiatrist Carl Jung, divided all personalities into introverts and extraverts. The introvert tends to withdraw into himself, particularly in times of emotional stress and conflict; he tends to by shy and prefers to work alone.
The introvert may take to the speaking platform in support of some movement to which he is strongly committed, but even then he is impelled from within. The extravert under stress seeks the company of others. He is likely to be very sociable, a “hail fellow well met,” and tends to choose occupations that permit him to deal directly with people, such as sales or promotional work.
You probably know a “typical introvert” and a “typical extravert.” But it is also likely that most of your friends fall somewhere between the two extremes. This is one of the major problems of type theories. Most typologies, whether they are based on physical or psychological characteristics, involve a continuum of individual differences rather than discrete types. Type theories are appealing because they provide a simple way of looking at personality, but, in actually, personality if far more complex.
Each person reacts in his own way to social pressures. Personal differences in behaviour may result from biological differences-differences in physical strength, sensitivity, and endurance. They may result from the rewards and punishments imposed by the parents and the type of behaviour modeled by them. Even though he may not resemble them, a child shows the influences of his parents.
Beyond a unique biological inheritance and the specific ways in which the culture is transmitted, the individual is shaped by particular experiences. An illness with a long convalescence may provide satisfactions in being cared for and waited upon that profoundly affect the personality structure. Death of a parent may disrupt the usual identifications. Accidents, opportunities for heroism, winning a contest, moving to another part of the country-countless such experiences are relevant to development but are not predictable from the culture, although, of course, their effects are partly determined by the culture.