Atman and Brahman: the core claim

Two words carry almost the entire weight of Advaita Vedanta: Atman and Brahman. Atman means the innermost self — not your body, not your personality, not even your thoughts or emotions, but the bare awareness that's present underneath all of those, the thing that's aware of the body, the thoughts, the emotions, without itself being any of them. Brahman means the single, infinite, non-dual reality that underlies the entire universe — the "ground of being," if that phrase helps, though Advaita would say even that undersells it, since Brahman isn't a background behind things so much as the only thing that ultimately exists. Advaita's central teaching is that these two are not two things — they're identical. This is stated directly in the Chandogya Upanishad as "Tat Tvam Asi," usually translated "That thou art," or more plainly: you, at your deepest level, are that ultimate reality. Not connected to it, not a fragment or spark of it — identical with it, the way a single wave, if it could stop mistaking itself for something separate, would recognize itself as simply the ocean. This is easy to mishear as "my ego is God" — that's not the claim, and Advaita is explicit about the difference. The ego — the sense of "me, this particular person, with this history and these preferences" — is exactly the layer that's said to be a false identification, not the Atman itself. The claim isn't that your personality is divine; it's that underneath the personality, the bare awareness you actually are, once you stop confusing it with the personality wrapped around it, is not separate from the one reality everything else is made of either. That identity — Atman is Brahman — is what Advaita means by "non-dual." It's not a metaphor about unity in a poetic sense; it's presented as a literal claim about what you most fundamentally are.