Tat Tvam Asi. This Sanskrit phrase, meaning "Thou art that," is used in Hinduism as a mantra to represent the fundamental identity between the microcosm and the macrocosm. Tat refers to brahman, the universal principle; tvam (thou) is the ātman, the individualized aspect thereof. From a Hindu standpoint the phrase points to the altruistic attitude of the ethical person, who subordinates individual self to the self of all others. The phrase occurs in the Chāndogya Upanishad, 6,8,6.

Geddes MacGregor, Dictionary of Religion and Philosophy, New York: Paragon House, 1989