Some postcolonial theorists have argued that the idea of a single system of belief known as "Hinduism" is a creation of nineteenth-century British imperialists. Andrew J. Nicholson introduces another perspective: although the idea of a unified Hindu identity is not as ancient as many Hindus claim, it has its roots in the innovations of South Asian philosophy from the fourteenth to seventeenth centuries. Thinkers treated the philosophies of Vedanta, Samkhya, and Yoga and the deities Visnu, Siva, and Sakti as all belonging to a single system of belief and practice& mdash;rivers leading into the ocean of Brahman, the ultimate reality. Drawing on the work of philosophers from late medieval Vedanta traditions, including Vijnanabhiksu, Madhava, and Madhusudana Sarasvati, Nicholson shows how thinkers portrayed Vedanta philosophy as the ultimate unifier of diverse belief systems. This late medieval project paved the way for later visionaries, such as Vivekenanda, Radhakrishnan, and Gandhi, whose teachings promoted the idea that all world religions belonged to a single spiritual unity. Nicholson revisits monism and dualism, theism and atheism, and orthodoxy and heterodoxy, and he critiques such formulas as "the six orthodox systems" that have worked their way into modern thinking about Indian philosophy.