Theories of conditioning and learning have a number of historical roots within the philosophical doctrine of associationism. Associationism holds that simple associations between ideas are the basis of human thought and knowledge, and that complex ideas are combinations of these simple associations. Associationism can be traced as far back as Aristotle (384-322 B.C.), who proposed three factors—contrast, similarity, and contiguity, or nearness in space or time of occurrence—that determine if elements, things, or ideas will be associated together.
British associationist-empiricist philosophers of the 1700s and 1800s such as Locke, Hume, and Mills, held that the two most fundamental mental operations are association and sensation. As empiricists, they believed all knowledge is based on sensory experience, and complex mental processes such as language, or ideas such as truth, are combinations of directly experienced ideas. This school of thought differs from nativist views which generally stress inherited genetic influences on behavior and thought. According to these views, we are born with certain abilities or predispositions that actively shape or limit incoming sensory experience. For example, Plato (c. 427–347 B.C.) believed we are born with certain pre-formed ideas as did Rene Descartes (1596-1650). Many contemporary psychologists believe we are born with certain skill-based potentials and capacities such as those involved in language. In the 1880s the German psychologist Hermann Ebbinghaus brought this philosophical doctrine within the realm of scientific study by creating experimental methods for testing learning and memory that were based on associationistic theory. Associationist ideas are also at the root of behaviorism, a highly influential school of thought in psychology that was begun by John B. Watson in the 1910s. And conditioning experiments enabling the standardized investigation of associations formed, not between ideas, but between varying stimuli, and stimuli and responses, are also based on associationism.