THE PURPOSE of this paper is to consider the similarities among a number of concepts which arose relatively independently in diverse fields of behavioral research. There are two major elements which unite these concepts: first, they derive from the interrelated problem of characterizing both stimuli and individuals; and second, the experimental designs by which the concepts are tested are similar. In particular, we will develop the thesis that the psychophysiological principle of response specificity is a unifying principle because it collects so many seemingly unrelated concepts. Both the various forms of specificity and some of the experimental variables necessary to demonstrate their existence will be described, and then an attempt will be made to show that many different concepts in psychology and psychiatry can be related to one another through the principle of specificity.
The most general division of the principle