Beginning with Vedantic Hindu philosophy, the Ātman - Sanskrit (masculine nominative singular: Ātmā) is regarded as an underlying metaphysical self. It is first seen in its current Hindu usage in the Upanishads, some of which date back to 1000 BC. The word "Atman" (pronounced in Sanskrit like "Atma") is interpreted by some schools as the "Main Essence" of man, as his Highest Self. "A" in this word is a negative particle. One popular, albeit apocryphal, etymology has it that the 'tma' of "atma" "Tma" means "darkness" in light of the word "tamas" - "darkness, ignorance or inertia", "spiritual darkness" - has the same root. Therefore “A-tma” or "Atman" means "opposite to darkness", "shining".

Advaita philosophers believe that individual "personal" souls exist as Maya only. Dvaita philosophy claims that there is an eternal plurality of souls as per Bhagavad Gita 2.12.

Advaita posits an ultimate ātman (synonymous with Brahman) as the all-pervading soul of the universe: the universal life-principle, the animator of all organisms, and the world-soul. This view is of a sort of panentheism (not pantheism) and thus is sometimes not equated with the single creator God of monotheism. Dvaita calls the all-pervading aspect of Brahman Paramatman (Paramatma), quantitatively different from individual Atman.

Identification of individual souls, or jiva-atmas, with the 'One Atman' is the monistic Advaita Vedanta position, which is critiqued by dualistic/theistic Dvaita Vedanta (which claims reality for both a God functioning as the ultimate metaphorical "soul" of the universe, and for actual individual "souls" as such) and compromise schools like Vishishtadvaita Vedanta. The 'dvaita' (or dualist) schools, therefore, in contrast to Advaita, advocate a exclusive monotheistic position wherein Brahman is made synonymous with Vishnu.

By contrast, Jiva is the psychological or phenomenological self, the "I" which appears as the subject of verbs. The jiva is typically regarded as having its freedom limited by the triple bond of anava (ego), karma (action) and maya (illusion).

Non-technical uses of ātman

Ātman is also sometimes used non-technically to refer to the commonsense self (i.e., the individual as opposed to other beings or to the environment). It is frequently used to reform compounds in this capacity, both in Hindu and Buddhist writings. Upanishadic writers would frequently stress the difference between oneself (ego-bound) and the True Self (atman and Atman).

Buddhism

A major departure from the Hindu conception of atman was to be found in Buddhism. Both negation (in anatta/anatman) and redefining (Atman (Buddhism)) of atman yielded different philosophical outlooks on the concept of "I" and the "self." Jainism also believes in the concept of atman.