Psychology, scientific study of behavior and experience—that is, the study of how human beings and animals sense, think, learn, and know. Modern psychology is devoted to collecting facts about behavior and experience and systematically organizing such facts into psychological theories. These theories aid in understanding and explaining people’s behavior and sometimes in predicting and influencing their future behavior.
Psychology, historically, has been divided into many subfields of study; these fields, however, are interrelated and frequently overlap. Physiological psychologists, for instance, study the functioning of the brain and the nervous system, and experimental psychologists devise tests and conduct research to discover how people learn and remember. Subfields of psychology may also be described in terms of areas of application. Social psychologists, for example, are interested in the ways in which people influence one another and the way they act in groups. Industrial psychologists study the behavior of people at work and the effects of the work environment. School psychologists help students make educational and career decisions. Clinical psychologists assist those who have problems in daily life or who are mentally ill.
History. The science of psychology developed from many diverse sources, but its origins as a science may be traced to ancient Greece.
Philosophical Beginnings. Plato and Aristotle, as well as other Greek philosophers, took up some of the basic questions of psychology that are still under study: Are people born with certain skills, abilities, and personality, or do all these develop as a result of experience? How do people come to know the world? Are certain ideas and feelings innate, or are they all learned?
Such questions were debated for many centuries, but the roots of modern psychological theory are found in the 17th century in the works of the French philosopher Ren Descartes and the British philosophers Thomas Hobbes and John Locke. Descartes argued that the bodies of people are like clockwork machines, but that their minds (or souls) are separate and unique. He maintained that minds have certain inborn, or innate, ideas and that these ideas are crucial in organizing people’s experiencing of the world. Hobbes and Locke, on the other hand, stressed the role of experience as the source of human knowledge. Locke believed that all information about the physical world comes through the senses and that all correct ideas can be traced to the sensory information on which they are based.
Most modern psychology developed along the lines of Locke’s view. Some European psychologists who studied perception, however, held onto Descartes’s idea that some mental organization is innate, and the concept still plays a role in theories of perception and cognition.
Against this philosophical background, the field that contributed most to the development of scientific psychology was physiology—the study of the functions of the various organ systems of the body. The German physiologist Johannes Miller tried to relate sensory experience both to events in the nervous system and to events in the organism’s physical environment. The first true experimental psychologists were the German physicist Gustav Theodor Fechner and the German physiologist Wilhelm Wundt. Fechner developed experimental methods for measuring sensations in terms of the physical magnitude of the stimuli producing them. Wundt, who in 1879 founded the first laboratory of experimental psychology in Leipzig, Germany, trained students from around the world in this new science.
Physicians who became concerned with mental illness also contributed to the development of modern psychological theories. Thus, the systematic classification of mental disorders developed by the German psychiatric pioneer Emil Kraepelin remains the basis for methods of classification that are now in use. Far better known, however, is the work of Sigmund Freud, who devised the system of investigation and treatment known as psychoanalysis. In his work, Freud called attention to instinctual drives and unconscious motivational processes that determine people’s behavior. This stress on the contents of thought, on the dynamics of motivation rather than the nature of cognition in itself, exerted a strong influence on the course of modern psychology.