 An inspiration for Schopenhauer’s view that ideas are like inert objects is George Berkeley (1685–1753), who describes ideas in this deactivated way in his A Treatise Concerning the Principles of Human Knowledge (1710) [Section 25]. A primary inspiration for Schopenhauer’s double-aspect view of the universe is Baruch (Benedict) de Spinoza (1632–1677), who developed a similarly-structured metaphysics, and who Schopenhauer had studied in his early years before writing his dissertation. A subsequent, but often highlighted inspiration is from the Upanishads (c. 900–600 BCE) which also expresses a double-aspected view of the universe as having objective and subjective aspects, referred to respectively as Brahman and Atman. 