Schopenhauer argued for the oneness of all reality. How then can we account for differences which exist between objects in reality? Schopenhauer argued that for one thing to be different from another at all there must be "differentiation." He contended that these differences apply only to things in this world. He also contended that this differentiation has to do with time, space or both time and space. Therefore, whatever there is outside of this world must be one and is consequently undifferentiated according to Schopenhauer.
Schopenhauer differed from Kant in that he argued that Kant was wrong in talking about "things" in the plural. Schopenhauer argued that ultimate reality is one, though things appear to be differentiated due to time or space or perhaps both in this world. This development in Schopenhauer's though represents a unique shift. With this concept of the oneness of all reality, Schopenhauer moved in toward belief in Hinduism and Buddhism. Like Schopenhauer, these religious movements advocated that behind all we observe there is one ultimate reality. It should be pointed out, however, that Schopenhauer got this idea of the oneness of all reality not from Buddhism or Hinduism, but from his own contemplation of reality and Western philosophy. He later recognized that his conception of the oneness of all reality paralleled the beliefs of Buddhism and Hinduism.
