poverty of the stimulus a psychological phenomenon exhibited when behavior is stimulusunbound, and hence the immediate stimulus characterized in straightforward physical terms does not completely control behavior. Human beings sort stimuli in various ways and hosts of influences seem to affect when, why, and how we respond – our background beliefs, facility with language, hypotheses about stimuli, etc. Suppose a person visiting a museum notices a painting she has never before seen. Pondering the unfamiliar painting, she says, ‘an ambitious visual synthesis of the music of Mahler and the poetry of Keats.’ If stimulus (painting) controls response, then her utterance is a product of earlier responses to similar stimuli. Given poverty of the stimulus, no such control is exerted by the stimulus (the painting). Of course, some influence of response must be conceded to the painting, for without it there would be no utterance. However, the utterance may well outstrip the visitor’s conditioning and learning history. Perhaps she had never before talked of painting in terms of music and poetry. The linguist Noam Chomsky made poverty of the stimulus central to his criticism of B. F. Skinner’s Verbal Behavior (1957). Chomsky argued that there is no predicting, and certainly no critical stimulus control of, much human behavior. G.A.G.