Verbal Behavior: Extended Edition. Chapter 3: The Mand. Quote 1

A “mand” … may be defined as a verbal operant in which the response is reinforced by a characteristic consequence and is therefore under the functional control of relevant conditions of deprivation or aversive stimulation … In particular, and in contrast with other types of verbal operants to be discussed later, the response has no specified relation to a prior stimulus. (pp. 35-36)