Cumulative Record. Chapter 28: The Operational Analysis of Psychological Terms. Quote 20

We may generalize the conditions responsible for the standard “semantic” relation between a verbal response and a particular stimulus without going into reinforcement theory in detail … . The reinforcement of the response “red,” for example, is contingent upon the presence of a red object. (The contingency need not be invariable.) A red object then becomes a discriminative stimulus, an “occasion,” for the successful emission of the response “red.” (p. 419)