Verbal Behavior
Chapter three of Skinner's work, "Verbal Behavior", discusses a functional relationship called the mand. A mand is a form of verbal behavior that is controlled by deprivation, satiation, or what is now called motivating operations (MO), as well as a controlling history. An example of this would be asking for water when one is water deprived ("thirsty"). It is tempting to say that a mand "describes its reinforcer", which it sometimes does. But many mands have no correspondence to the reinforcer. For example, a loud knock may be a mand "open the door" and a servant may be called by a hand clap as much as a child might "ask for milk."