The study of gesture has a long history. The earliest books devoted exclusively to it appeared at the beginning of the 17th century. In the 18th century, especially in France, gesture was looked upon as having great relevance for the understanding of the natural origin of language and the nature of thought. Condillac and Diderot, in particular, wrote about it quite extensively. In the 19th century, gesture continued to command serious attention. Edward Tylor and Wilhelm Wundt both dealt with it at length. They believed that its study would throw light upon the transition from spontaneous, individual expression to the development of codified language systems. For much of this century, however, the study of gesture appears to have languished. The question of language origins, which has always provided an important justification for its study, fell into disrepute. Psychology neglected gesture because it seemed too much connected with deliberate action and social convention to be of use for the understanding of the irrational or to be easily accommodated in terms of behavioristic doctrine. It has been neglected by linguists because it has seemed too much a matter of individual expression. In any case it could not be accommodated into the rigorous systems of phonology and grammar with which linguists were preoccupied. Even the growth of interest in what came to be known as "nonverbal communication" did not stimulate the study of gesture as one might have expected. This was because the preoccupation here has been with how behavior functions communicatively in the regulation of interaction and in the management of interpersonal relations. Gesture is too much a part of conscious expression and too closely connected with the verbal for it to be of central relevance here.