The concepts of action and reaction before Newton have received so little attention from historians that the unwary student might easily get the impression that Newton was the first to concern himself seriously with the problem. In fact, the subject had a long prehistory extending back to Aristotle and it was actively discussed by physicists during the half-century preceding the publication of Principia mathematica in 1687. Although there is no evidence that Newton himself was much influenced by the views of (...) others on the subject, they formed a part of the intellectual background of the Principia which should not be ignored. (shrink)