A branch of psychology concerned with developing a scientifically defensible model or view of human nature—in the modern parlance, a general theory of behavior.
Most personality theories can be classified in terms of two broad categories, depending on their underlying assumptions about human nature. On the one hand, there are a group of theories that see human nature as fixed, unchanging, deeply perverse, and self-defeating. These theories emphasize self-understanding and resignation; in the cases of Freudian psychoanalysis and existentialism, they also reflect a distinctly tragic view of life—the sources of human misery are so various that the best that can be hoped for is to control some of the causes of suffering. On the other hand, there are a group of theories that see human nature as plastic, flexible, and always capable of growth, change, and development. Human nature is basically benevolent; therefore bad societies are the source of personal misery. Social reform will produce human happiness if not actual perfection. These theories emphasize self-expression and self-actualization—in the cases of Carl Rogers and Abraham Maslow, they reflect a distinctly optimistic and romantic view of life.