This chapter explores some answers to the first question: these questions were, first, 'What is the fundamental nature of reality? What is the identity of the true self?' The two most important themes in the Upanisads are the nature of the ultimately real and the identity of the true self. The early Upanisads mark a transitional phase away from the ancient Vedic sacrificial religion to a religion which was more concerned with the inner life. The Upanisads also promoted the idea that the realization that atman is Brahman is not principally an intellectual realization. Pluralists about ontology hold that monism and dualism are both false because reality is constituted by a plurality of different kinds of items that cannot be reduced to just one or two types of entity or substance. The dualism of other darsanas, such as the Sakhya can be regarded as a compromise between monism and pluralism.