The Upanishads

The philosophical capstone of the Vedic corpus. Upanishad literally means "sitting down near" — the student sitting at the teacher's feet to receive the inner teaching. The Upanishads are Vedanta — "the end of the Veda" — both in textual position (they appear at the close of each Vedic shakha) and in philosophical sense (they are where Vedic ritual moves into Vedic metaphysics). Composed between roughly the 8th and 3rd centuries BCE, the Upanishads are the founding texts of Indian philosophy and one of the four or five most influential bodies of philosophical literature in human history.

Schopenhauer wrote of the Brihadaranyaka Upanishad: "It has been the solace of my life. It will be the solace of my death." Emerson, Thoreau, Yeats, Eliot, Schrödinger, Oppenheimer, Heisenberg, Huxley, Jung all drew on the Upanishads in their own work. They are why Vedanta is the most globally circulated of all Hindu philosophical traditions.

The principal Upanishads

The Hindu tradition recognises 108 Upanishads (the Muktika Upanishad catalogue), but eleven are the Mukhya Upanishads — the principal ones — on which Shankara, Ramanuja, Madhva, and the other Vedanta acharyas wrote commentaries:

Upanishad	Veda	Length	Defining teaching
Isha	Yajurveda	18 verses	Ishavasyam idam sarvam — "all this is pervaded by the Lord"
Kena	Samaveda	35 verses	Brahman is what the eye cannot see but by which the eye sees
Katha	Yajurveda	119 verses	Nachiketa's dialogue with Yama; the soul as the rider, the body as the chariot
Prashna	Atharvaveda	6 questions	The six questions to rishi Pippalada on origins, life, and breath
Mundaka	Atharvaveda	64 verses	The two birds on the tree — one eating fruit, one watching
Mandukya	Atharvaveda	12 verses	AUM — the four states of consciousness — the shortest and densest
Taittiriya	Yajurveda	3 chapters	The five sheaths (pancha-kosha) of the self
Aitareya	Rigveda	33 verses	The Atman as the creative source
Chandogya	Samaveda	8 chapters	Tat tvam asi — "that thou art" — Uddalaka teaching Shvetaketu
Brihadaranyaka	Yajurveda	6 chapters	The longest and most philosophically rich; Yajnavalkya's dialogues
Shvetashvatara	Yajurveda	6 chapters	The Upanishad closest to theistic-devotional formulation

The four Mahavakyas

Vedanta crystallises the entire Upanishadic teaching into four "great sayings," one drawn from each Veda:

Mahavakya	Veda	Source
Prajnanam Brahma ("Consciousness is Brahman")	Rigveda	Aitareya Upanishad 3.3
Aham Brahmasmi ("I am Brahman")	Yajurveda	Brihadaranyaka Upanishad 1.4.10
Tat Tvam Asi ("That thou art")	Samaveda	Chandogya Upanishad 6.8.7
Ayam Atma Brahma ("This Self is Brahman")	Atharvaveda	Mandukya Upanishad 2

The Mahavakyas are the operational summary: the inner self (atman) and the cosmic ground (Brahman) are identical. Liberation (moksha) is the direct realisation of that identity. All Vedanta schools agree on the formulation; they disagree on the metaphysical interpretation. Advaita (Shankara): the identity is non-dual — there is one reality and the apparent plurality is maya. Vishishtadvaita (Ramanuja): the identity is qualified — atman and Brahman are related as soul and body of a single divine person. Dvaita (Madhva): the identity is symbolic — atman and Brahman are eternally distinct, and liberation is loving union, not identity.

Signature passages

The Nasadiya Sukta is in the Rigveda; the Upanishadic equivalent is the Brihadaranyaka 3.8 dialogue between Yajnavalkya and Gargi — a male sage and a female philosopher debating the nature of the absolute in front of the assembled court of King Janaka. Gargi presses Yajnavalkya through five increasingly metaphysical questions until he answers: the Imperishable (akshara) is that on which all of space-time is woven, and "whoever does not know this dies a wretch." It is the most rigorous philosophical exchange in pre-Socratic world literature.
Brihadaranyaka 4.5 — Yajnavalkya's dialogue with his wife Maitreyi: "Verily, not for love of the husband is the husband dear, but for love of the Atman; verily not for love of the wife is the wife dear, but for love of the Atman." The foundational statement of metaphysical priority.
Katha 2.18–22 — "The Atman is not born; nor does it die; it is not from anywhere, nor did anything become it… When the body is slain, the Atman does not slay; it is not slain." Krishna quotes this directly in Gita 2.19–20.
Mandukya — twelve verses, eleven syllables: AUM (A + U + M + silence) is the four states of consciousness (waking, dream, deep sleep, turiya — pure consciousness). Gaudapada's Karika (7th c) commentary on the Mandukya is the foundational text for Advaita Vedanta and Shankara's teacher's teacher.

The bridge to philosophy of mind

The Upanishadic doctrine of consciousness — that Atman is the prajna (pure awareness) which makes all knowing possible, not itself an object of knowing — anticipates by two and a half millennia the contemporary "hard problem of consciousness" articulated by David Chalmers. The Upanishadic move is not to explain consciousness in terms of matter (which is the failed reductionist programme) but to take consciousness as primary and ask how matter appears within it. This is the same move that Schopenhauer, Henri Bergson, and more recently Donald Hoffman make. The Upanishads got there first.

Modern transmission

Shankara (8th c) — wrote Bhashyas on the principal Upanishads, the Brahma Sutra, and the Bhagavad Gita. The Advaita system as articulated by Shankara is the most globally circulated version of Vedanta. See person shankaracharya.
Vivekananda (1893 Chicago Parliament of Religions) — introduced Vedanta as a global philosophical tradition to the West.
Aurobindo — The Life Divine, the Synthesis of Yoga, and his translations of the Isha and Kena Upanishads.
Ramana Maharshi — embodied the Mandukya Upanishad's teaching that the self-inquiry "Who am I?" dissolves into the Atman.

Abhishek