HISTORIANS of psychology are almost unanimously agreed on one point: that psychology is a relatively new science. There may be some disagreement as to when it started--with Weber, or Fechner, or Wundt, or James--but there is almost no dissent from the proposition that psychology as a scientific discipline is less than one and one-half centuries old. Many earlier writers are often discussed in histories of psychology, but invariably they are called speculators, or philosophers, as opposed to scientists. We believe that (...) this is an incorrect appraisal of the career of psychological research. To demonstrate our point, we propose to show how one key psychological idea from Descartes' work has had an extensive and robust scientific history. If it is true that this Cartesian idea has had great influence in science, then many claims concerning the history of psychology will need to be reconsidered. Not everything which happened in psychology prior to the nineteenth century was speculative, nor is everything which happened later scientific. Even more importantly, if Descartes' idea has been of such central concern to several hundred years of research, it must be treated as an important claim about the way the world is, as a law of nature. (shrink)