Atman is the pratyagatman — the innermost self, the sakshi (witness) that remains unchanged through the three avastha (states of consciousness): jagrat (waking), svapna (dreaming), and sushupti (deep sleep). The Mandukya Upanishad identifies the Atman with turiya, the fourth state that pervades and transcends the other three, described as 'prapanchopashamam, shantam, shivam, advaitam' — the cessation of all phenomena, peaceful, auspicious, non-dual. Shankara's Vivekachudamani teaches that Atman is revealed not by acquisition of new knowledge but by the removal of avidya (ignorance) through the fourfold discipline of sadhana-chatushtaya: viveka (discrimination), vairagya (dispassion), shat-sampat (six virtues), and mumukshutva (burning desire for liberation).