  The behaviorist psychologist B.F. Skinner was the first theorist to  propose a fully fledged theory of language acquisition in his book,  Verbal Behavior (Skinner 1957). His theory of learning was  closely related to his theory of linguistic behavior itself. He  argued that human linguistic behavior (that is, our own utterances  and our responses to the utterances of others) is determined by two  factors: (i) the current features of the environment impinging on the speaker, and (ii) the speaker's history of reinforcement (i.e., the  giving or withholding of rewards and/or punishments in response to  previous linguistic behaviors). Eschewing talk of the mental as  unscientific, Skinner argued that ‘knowing’ a language is really just a matter of having a certain set of behavioral  dispositions: dispositions to say (and do) appropriate things in  response to the world and the utterances of others. Thus, knowing  English is, in small part, a matter of being disposed to utter  “Please close the door!” when one is cold as a result of  a draught from an open door, and of being disposed (other things  being equal) to utter “OK” and go shut a door in response to someone else's utterance of that formula.