Verbal Behavior: Extended Edition. Chapter 5: The Tact. Quote 3

It may be tempting to say that in a tact the response “refers to,” “mentions,” “announces,” “talks about,” “names,” “denotes,” or “describes” its stimulus. But the … only useful functional relation is expressed in the statement that the presence of a given stimulus raises the probability of occurrence of a given form of response. This is also the essence of the tact. (p. 82)