Tat Tvam Asi (Devanagari: तत्त्वमसि), a Sanskrit phrase, translated variously as "That art thou," "That thou art," "Thou art that," "You are that," or "That you are," is one of the Mahāvākyas (Grand Pronouncements) in VedanticSanatana Dharma. It originally occurs in the Chandogya Upanishad 6.8.7, in the dialogue between Uddalaka and his son Śvetaketu; it appears at the end of a section, and is repeated at the end of the subsequent sections as a refrain. The meaning of this saying is that the Self - in its original, pure, primordial state - is wholly or partially identifiable or identical with the Ultimate Reality that is the ground and origin of all phenomena.
Major Vedantic schools offer different interpretations of the phrase:
Advaita - absolute equality of 'tat', the Ultimate Reality, Brahman, and 'tvam', the Self, Atman.
Shuddhadvaita - oneness in "essence" between 'tat' and individual self; but 'tat' is the whole and self is a part.
Dvaitadvaita - equal non-difference and difference between the individual self as a part of the whole which is 'tat'.
Dvaita of Madhvacharya - “Sa atmaa-tat tvam asi” in Sanskrit is actually “Sa atma-atat tvam asi” or “Atman, thou art not that”. In refutation of Mayavada (Mayavada sata dushani), text 6, 'tat tvam asi" is translated as "you are a servant of the Supreme (Vishnu)"
Acintya Bheda Abheda - inconceivable oneness and difference between individual self as a part of the whole which is 'tat'.
The Vedas form the fundamental source text for everything in Hinduism. Each of the four Vedas has metaphysical speculations, known as Upanishads, at the end. Among the various discussions in these Upanishads there are mahavakyas (Grand pronouncements), which are of foundational import and deep significance. Tat tvam asi (meaning, That Thou Art) is one such. This is from Chandogya Upanishad. Different schools of philosophy interpret such fundamental statements in significantly different ways, so as to be consistent with their own philosophical thought. Below is the interpretation of the Vishishtadvaita school.
^Raphael, Edwin (1992). The pathway of non-duality, Advaitavada: an approach to some key-points of Gaudapada's Asparśavāda and Śaṁkara's Advaita Vedanta by means of a series of questions answered by an Asparśin. Iia: Philosophy Series. Motilal Banarsidass. ISBN 81-208-0929-7, ISBN 978-81-208-0929-1. Source:  (accessed: Tuesday April 27, 2010), p.Back Cover