There is no doubt of the enormous influence Descartes has exercised from his own day to ours. But his relation to modern philosophy is not that of father to son, nor of architect to palace, nor of planner to city. Rather, in the history of philosophy his position is like that of the waist of an hourglass. As the sand in the upper chamber of such a glass reaches its lower chamber only through the slender passage between the two, so too ideas that had their origin in the Middle Ages have reached the modern world through a narrow filter: the compressing genius of Descartes.