Skinner, B. F. (1950). Are Theories of Learning Necessary? Psychological Review, 57, 193-216.
(Beginning of Paper)
Certain basic assumptions, essential to any scientific activity, are sometimes called theories. That nature is orderly rather than capricious is an example. Certain statements are also theories simply to the extent that they are not yet facts. A scientist may guess at the result of an experiment before the experiment is carried out. The prediction and the later statement of result may be composed of the same terms in the same syntactic arrangement, the difference being in the degree of confidence. No empirical statement is wholly non-theoretical in this sense, because evidence is never complete, nor is any prediction probably ever made wholly without evidence. The term "theory" will not refer here to statements of these sorts but rather to any explanation of an observed fact which appeals to events taking place somewhere else, at some other level of observation, described in different terms, and measured, if at all, in different dimensions.
Three types of theory in the field of learning satisfy this definition...