Psychology seems to mean many things to many people. In everyday life the word psychology has a variety of meanings with mentalistic, behavioristic, or abnormal implications. The popular media seem to reinforce this perception. For example, we often hear the words psychological, psychiatric, and psychoanalytic equated and used interchangeably. We often read or see research results on smoking or drug hazards conducted by psychologists but described as medical research. Or we see instances where a psychologist, using “armchair” methodology, responds with profound advice in a newspaper to a reader in distress. Nor does the college- level introductory course to psychology necessarily dispel the confusion. Those who have taken such courses may have dim, confused recollections of IQ tests, dogs salivating, hierarchies of anxiety, the Oedipus complex, figure-ground reversals, rats running through a maze, heart rate control, peer group influence, and so on. Similarly, listing the range of positions held by psychologists does not resolve the confusion. We find psychologists in hospitals and community mental health centers, in advertising and industry, in government and the military, and in universities.
Whereas the diversity of modern psychology is a source of bewilderment, psychology's range of study is justifiably broad. As a formal, independent discipline studied and taught in universities, psychology has been in existence for only just over a century. However, we should recognize that people have been “psychologizing” since they first began to wonder about themselves. The long history of theories and models of psychology slowly evolved, mostly within philosophy, until the nineteenth century, when the methodological spirit of science was applied to the study of psychology and the formal discipline of psychology appeared in Western intellectual institutions.
The emergence of psychology as a formal discipline takes us to the problem of science. Generally, science is defined as the systematic acquisition of knowledge. However, from a narrower perspective, the acquisition of knowledge is limited to observations validated by our senses. That is, we must see, hear, touch, taste, or smell events to confirm their existence as scientific data. This type of science is called empiricism, and its most controlled application is called the experimental method, in which variables are manipulated and measured. Toward the end of the nineteenth century, this narrower, empirical definition of science linked up with a nineteenth-century model of what psychology should study to form the discipline of psychology.