There are some men who are counted great because they represent the
actuality of their own age, and mirror it as it is. Such an one
was Voltaire, of whom it was epigrammatically said, "he expressed
everybody's thoughts better than anybody." But there are other men who
attain greatness because they embody the potentiality of their own day
and magically reflect the future. They express the thoughts which
will be everybody's two or three centuries after them. Such an one was
Descartes.