psychology, scientific discipline that studies mental states and processes and behaviour in humans and other animals.
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.
(Read Sigmund Freud’s 1926 Britannica essay on psychoanalysis.)
Early history In Western culture, contributors to the development of psychology came from many areas, beginning with philosophers such as Plato and Aristotle. Hippocrates philosophized about basic human temperaments (e.g., choleric, sanguine, melancholic) and their associated traits. Informed by the biology of his time, he speculated that physical qualities, such as yellow bile or too much blood, might underlie differences in temperament (see also humour). Aristotle postulated the brain to be the seat of the rational human mind, and in the 17th century René Descartes argued that the mind gives people the capacities for thought and consciousness: the mind “decides” and the body carries out the decision—a dualistic mind-body split that modern psychological science is still working to overcome. Two figures who helped to found psychology as a formal discipline and science in the 19th century were Wilhelm Wundt in Germany and William James in the United States. James’s The Principles of Psychology (1890) defined psychology as the science of mental life and provided insightful discussions of topics and challenges that anticipated much of the field’s research agenda a century later.