Personality type refers to the psychological classification of different types of individuals. Personality types are sometimes distinguished from personality traits, with the latter embodying a smaller grouping of behavioral tendencies. Types are sometimes said to involve qualitative differences between people, whereas traits might be construed as quantitative differences. According to type theories, for example, introverts and extraverts are two fundamentally different categories of people. According to trait theories, introversion and extraversion are part of a continuous dimension, with many people in the middle.
Effective personality typologies reveal and increase knowledge and understanding of individuals, as opposed to diminishing knowledge and understanding as occurs in the case of stereotyping. Effective typologies also allow for increased ability to predict clinically relevant information about people and to develop effective treatment strategies. There is an extensive literature on the topic of classifying the various types of human temperament and an equally extensive literature on personality traits or domains. These classification systems attempt to describe normal temperament and personality and emphasize the predominant features of different temperament and personality types; they are largely the province of the discipline of psychology. Personality disorders, on the other hand, reflect the work of psychiatry, a medical specialty, and are disease-oriented. They are classified in the Diagnostic and Statistical Manual (DSM), a product of the American Psychiatric Association.
The term type has not been used consistently in psychology and has become the source of some confusion. Furthermore, because personality test scores usually fall on a bell curve rather than in distinct categories, personality type theories have received considerable criticism among psychometric researchers. One study that directly compared a "type" instrument (the MBTI) to a "trait" instrument (the NEO PI) found that the trait measure was a better predictor of personality disorders. Because of these problems, personality type theories have fallen out of favor in psychology. Most researchers now believe that it is impossible to explain the diversity of human personality with a small number of discrete types. They recommend trait models instead, such as the five-factor model.
One of the more influential ideas originated in the theoretical work of Carl Jung as published in the book Psychological Types. The original German language edition, Psychologische Typen, was first published by Rascher Verlag, Zurich, in 1921. Typologies such as Socionics, the MBTI assessment, and the Keirsey Temperament Sorter have roots in Jungian theory.
Jung's interest in typology grew from his desire to reconcile the theories of Sigmund Freud and Alfred Adler, and to define how his own perspective differed from theirs. Jung wrote, "In attempting to answer this question, I came across the problem of types; for it is one's psychological type which from the outset determines and limits a person's judgment." (Jung,  1989:207) He concluded that Freud's theory was extraverted and Adler's introverted. (Jung,  1971: par. 91) Jung became convinced that acrimony between the Adlerian and Freudian camps was due to this unrecognized existence of different fundamental psychological attitudes, which led Jung "to conceive the two controversial theories of neurosis as manifestations of a type-antagonism." (Jung, 1966: par. 64)
In the book Jung categorized people into primary types of psychological function.
Jung proposed the existence of two dichotomous pairs of cognitive functions:
Jung went on to suggest that these functions are expressed in either an introverted or extraverted form.:17
According to Jung, the psyche is an apparatus for adaptation and orientation, and consists of a number of different psychic functions. Among these he distinguishes four basic functions:
Thinking and feeling functions are rational, while sensation and intuition are nonrational. According to Jung, rationality consists of figurative thoughts, feelings or actions with reason -- a point of view based on objective value, which is set by practical experience. Nonrationality is not based in reason. Jung notes that elementary facts are also nonrational, not because they are illogical but because, as thoughts, they are not judgments.
Analytical psychology distinguishes several psychological types or temperaments.
Extraversion means "outward-turning" and introversion means "inward-turning". These specific definitions vary somewhat from the popular usage of the words.
The preferences for extraversion and introversion are often called attitudes. Each of the cognitive functions can operate in the external world of behavior, action, people, and things (extraverted attitude) or the internal world of ideas and reflection (introverted attitude).
People who prefer extraversion draw energy from action: they tend to act, then reflect, then act further. If they are inactive, their motivation tends to decline. To rebuild their energy, extraverts need breaks from time spent in reflection. Conversely, those who prefer introversion expend energy through action: they prefer to reflect, then act, then reflect again. To rebuild their energy, introverts need quiet time alone, away from activity.
An extravert's flow is directed outward toward people and objects, an introvert's is directed inward toward concepts and ideas. Contrasting characteristics between extraverts and introverts include the following:
The attitude type could be thought of as the flow of libido (psychic energy). The functions are modified by two main attitude types: extraversion and introversion. In any person, the degree of introversion or extraversion of one function can be quite different from that of another function.
Jung identified two pairs of psychological functions:
Sensation and intuition are the information-gathering (perceiving) functions. They describe how new information is understood and interpreted. Individuals who prefer the sensation function are more likely to trust information that is in the present, tangible and concrete: that is, information that can be understood by the five senses. They tend to distrust hunches, which seem to come "out of nowhere".:2 They prefer to look for details and facts. For them, the meaning is in the data. On the other hand, those who prefer the intuition function tend to trust information that is more abstract or theoretical, that can be associated with other information (either remembered or discovered by seeking a wider context or pattern). They may be more interested in future possibilities. They tend to trust those flashes of insight that seem to bubble up from the unconscious mind. The meaning is in how the data relates to the pattern or theory.
Thinking and feeling are the decision-making (judging) functions. The thinking and feeling functions are both used to make rational decisions, based on the data received from their information-gathering functions (sensing or intuition). Those who prefer the thinking function tend to decide things from a more detached standpoint, measuring the decision by what seems reasonable, logical, causal, consistent and matching a given set of rules. Those who prefer the feeling function tend to come to decisions by associating or empathizing with the situation, looking at it "from the inside" and weighing the situation to achieve, on balance, the greatest harmony, consensus and fit, considering the needs of the people involved.
As noted already, people who prefer the thinking function do not necessarily, in the everyday sense, "think better" than their feeling counterparts; the opposite preference is considered an equally rational way of coming to decisions (and, in any case, the MBTI assessment is a measure of preference, not ability). Similarly, those who prefer the feeling function do not necessarily have "better" emotional reactions than their thinking counterparts.
All four functions are used at different times depending on the circumstances. However, one of the four functions is generally used more dominantly and proficiently than the other three, in a more conscious and confident way. According to Jung the dominant function is supported by two auxiliary functions. (In MBTI publications the first auxiliary is usually called the auxiliary or secondary function and the second auxiliary function is usually called the tertiary function.) The fourth and least conscious function is always the opposite of the dominant function. Jung called this the "inferior function" and Myers sometimes also called it the "shadow function".:84
Jung's typological model regards psychological type as similar to left- or right-handedness: individuals are either born with, or develop, certain preferred ways of thinking and acting. These psychological differences are sorted into four opposite pairs, or dichotomies, with a resulting eight possible psychological types. People tend to find using their opposite psychological preferences more difficult, even if they can become more proficient (and therefore behaviorally flexible) with practice and development.
The four functions operate in conjunction with the attitudes (extraversion and introversion). Each function is used in either an extraverted or introverted way. A person whose dominant function is extraverted intuition, for example, uses intuition very differently from someone whose dominant function is introverted intuition.
The eight psychological types are as follows:
Jung theorized that the dominant function characterizes consciousness, while its opposite is repressed and characterizes unconscious behavior. Generally, we tend to favor our most developed dominant function, while we can broaden our personality by developing the others. Related to this, Jung noted that the unconscious often tends to reveal itself most easily through a person's least developed inferior function. The encounter with the unconscious and development of the underdeveloped functions thus tend to progress together.
When the unconscious inferior functions fail to develop, imbalance results. In Psychological Types, Jung describes in detail the effects of tensions between the complexes associated with the dominant and inferior differentiating functions in highly one-sided individuals.
The relationship between worry - the tendency of one's thoughts and mental images to revolve around and create negative emotions, and the experience of a frequent level of fear - and Jung's model of psychological types has been the subject of studies. In particular, correlational analysis has shown that the tendency to worry is significantly related to Jung's Introversion and Feeling dimensions. Similarly, worry has shown robust correlations with shyness and fear of social situations. The worrier's tendency to be fearful of social situations might make them appear more withdrawn.
Jung's model suggests that the superordinate dimension of personality is introversion and extraversion. Introverts are likely to relate to the external world by listening, reflecting, being reserved, and having focused interests. Extraverts on the other hand, are adaptable and in tune with the external world. They prefer interacting with the outer world by talking, actively participating, being sociable, expressive, and having a variety of interests. Jung (1921) also identified two other dimensions of personality: Intuition - Sensing and Thinking - Feeling. Sensing types tend to focus on the reality of present situations, pay close attention to detail, and are concerned with practicalities. Intuitive types focus on envisioning a wide range of possibilities to a situation and favor ideas, concepts, and theories over data. Thinking types use objective and logical reasoning in making their decisions, are more likely to analyze stimuli in a logical and detached manner, be more emotionally stable, and score higher on intelligence. Feeling types make judgments based on subjective and personal values. In interpersonal decision-making, feeling types tend to emphasize compromise to ensure a beneficial solution for everyone. They also tend to be somewhat more neurotic than thinking types. The worrier's tendency to experience a fearful affect, could be manifested in Jung's feeling type.
Three modern theories closely associated with Jung's personality types: