"[...] the history of philosophy deals with the doctrines conceived by philosophers, not philosophy in general in its entirety, nor the psychological evolution of each thinker in particular; therefore, its essential task, to which all others are subordinate, consists in penetrating and understanding doctrines, explaining them as well as possible, as the author himself would do, and presenting them in accordance with the spirit and, to a certain extent, the style of their author. (Ch. I, pp. 7-8)"