Psychohistory, as a science, will always be problem-centered, while history will always remain period-centered. They are simply two different tasks.

Historians are presumed to be unable to do psychology, which is mystical anyway, so they are forced to accept the most rational explanations... and it is on these that history is built.

Written history may, in the course of its narrative, use some of the laws established by the various sciences, but its own task remains that of relating the essential sequence of historical action and, qua history, to tell what happened, not why.

There is, for instance, only one page at the beginning of Runciman's three-volume History of the Crusades describing how the participants decided to begin four hundred years of wars, and then several thousand pages devoted to the routes, battles and other events which make up the history of the Crusades.