Personality is defined as an individual’s consistent patterns of feeling, thinking, and behaving. Early theories of personality, including phrenology and somatology, are now discredited, but there is at least some research evidence for physiognomy — the idea that it is possible to assess personality from facial characteristics.
Personalities are characterized in terms of traits, which are relatively enduring characteristics that influence our behaviour across many situations. Psychologists have investigated hundreds of traits using the self-report approach.
The utility of self-report measures of personality depends on their reliability and construct validity. Some popular measures of personality, such as the Myers-Briggs Type Indicator (MBTI), do not have reliability or construct validity and therefore are not useful measures of personality.
The trait approach to personality was pioneered by early psychologists, including Allport, Cattell, and Eysenck, and their research helped produce the Five-Factor (Big Five) Model of Personality. The Big Five dimensions are cross-culturally valid and accurately predict behaviour. The Big Five factors are also increasingly being used to help researchers understand the dimensions of psychological disorders.
A difficulty of the trait approach to personality is that there is often only a low correlation between the traits that a person expresses in one situation and those that he or she expresses in other situations. However, psychologists have also found that personality predicts behaviour better when the behaviours are averaged across different situations.
People may believe in the existence of traits because they use their schemas to judge other people, leading them to believe that traits are more stable than they really are. An example is the Barnum effect — the observation that people tend to believe in descriptions of their personality that supposedly are descriptive of them but could in fact describe almost anyone.
An important personality test is the Minnesota Multiphasic Personality Inventory (MMPI) used to detect personality and psychological disorders. Another approach to measuring personality is to use projective measures, such as the Rorschach Inkblot Test and the Thematic Apperception Test (TAT). The advantage of projective tests is that they are less direct, but empirical evidence supporting their reliability and construct validity is mixed.
There are behaviourist, social-cognitive, psychodynamic, and humanist theories of personality.
The psychodynamic approach to understanding personality, begun by Sigmund Freud, is based on the idea that all behaviours are predetermined by motivations that lie outside our awareness, in the unconscious. Freud proposed that the mind is divided into three components: id, ego, and superego, and that the interactions and conflicts among the components create personality. Freud also believed that psychological disorders, and particularly the experience of anxiety, occur when there is conflict or imbalance among the motivations of the id, ego, and superego and that people use defence mechanisms to cope with this anxiety.
Freud argued that personality is developed through a series of psychosexual stages, each focusing on pleasure from a different part of the body, and that the appropriate resolution of each stage has implications for later personality development.
Freud has probably exerted a greater impact on the public’s understanding of personality than any other thinker, but his theories have in many cases failed to pass the test of empiricism.
Freudian theory led to a number of followers known as the neo-Freudians, including Adler, Jung, Horney, and Fromm.
Humanistic theories of personality focus on the underlying motivations that they believe drive personality, focusing on the nature of the self-concept and the development of self-esteem. The idea of unconditional positive regard championed by Carl Rogers has led in part to the positive psychology movement, and it is a basis for almost all contemporary psychological therapy.
Personality traits of humans and animals are determined in large part by their genetic makeup. Personality is not determined by any single gene, but rather by the actions of many genes working together.
The role of nature and nurture in personality is studied by means of behavioural genetics studies including family studies, twin studies, and adoption studies. These studies partition variability in personality into the influence of genetics (known as heritability), shared environment, and nonshared environment. Although these studies find that many personality traits are highly heritable, genetics does not determine everything. The major influence on personality is nonshared environmental influences.
In addition to the use of behavioural genetics, our understanding of the role of biology in personality recently has been dramatically increased through the use of molecular genetics, the study of which genes are associated with which personality traits in animals and humans.