 Schopenhauer observed as an elementary condition, that to employ the principle of sufficient reason, we must think about something specific that stands in need of explanation. This indicated to him that at the root of our epistemological situation, we must assume the presence of a subject that thinks about some object to be explained. From this, he concluded that the general root of the principle of sufficient reason is the distinction between subject and object that must be presupposed as a condition for the very enterprise of looking for explanations (The Fourfold Root, Section 16) and as a condition for knowledge in general. 