Freudian theory made reason secondary: for Freud, the unconscious and its often socially unacceptable irrational motives and desires, particularly the sexual and aggressive, were the driving force underlying much of human behaviour and mental illness. Making the unconscious conscious became the therapeutic goal of clinicians working within this framework.

By the early 1960s the relevance of the Skinnerian approach for understanding complex mental processes was seriously questioned. The linguist Noam Chomsky’s critical review of Skinner’s theory of “verbal behaviour” in 1959 showed that it could not properly account for human language acquisition. It was one of several triggers for a paradigm shift that by the mid-1960s became the “cognitive revolution,” which compellingly argued against behaviourism and led to the development of cognitive science. In conjunction with concurrent analyses and advances in areas from computer science and artificial intelligence to neuroscience, genetics, and applications of evolutionary theory, the scientific study of the mind and mental activity quickly became the foundation for much of the evolving new psychological science in the 21st century.

The discipline of psychology is broadly divisible into two parts: a large profession of practitioners and a smaller but growing science of mind, brain, and social behaviour. The two have distinctive goals, training, and practices, but some psychologists integrate the two.