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(Sanskrit: "thou art that"), in Hindu philosophy, the famous expression of the relationship between the individual and the absolute. The statement is frequently repeated in the sixth chapter of the Chandogya Upanisad (c. 600 BC), as the teacher Uddalaka Aruni instructs his son in the nature of the supreme reality. The identity expressed in this judgment was variously interpreted by the different schools of the orthodox philosophy of Vedanta. The phrase was given its most literal interpretation by the 8th-9th-century thinker Sankara of the Advaita (Nondualist) school, for whom the statement was one of the great assertions fundamental to his doctrine.