The pure witnessing awareness in Advaita Vedanta. Present through waking, dream, and deep sleep. Not a subject who observes objects — the ground of all observation.
Right now, as you read this, something is aware. Not your name, not your history, not your mood today. Something simpler — the bare fact of awareness. That awareness has been present since the moment you woke up today. It was present yesterday. It is present in waking, when you are perceiving the world. It is present in dream, when the world you perceive is made by the mind. It is present in deep sleep, when perception stops — because you wake up knowing you slept. Something was there throughout.
Advaita calls this sākṣī — the witness. It is not a person. Not the ego, not the intellect, not the personality. It is the awareness within which all these appear and disappear. The ego appears in it. The thoughts appear in it. The emotions appear in it. The states of waking, dream, and sleep appear in it. The witness itself does not appear in anything — it is what appearance appears in.
This is the central claim of Advaita in practical terms: you are not what you observe in yourself. You are what observes. And what observes is not affected by what is observed — the way a cinema screen is not affected by the films projected on it.
Sākṣī (witness) is derived from sa (with) + akṣi (eye) — literally 'one who has eye-contact with.' In Advaita technical vocabulary, sākṣī refers specifically to consciousness in its aspect as the unchanging witness of all the modifications of the body-mind complex. The Māṇḍūkya's Turīya analysis is the most systematic account of the witness: Turīya is not a fourth state experienced after the other three but the witness of all three states — the unchanging awareness within which waking, dream, and deep sleep arise and subside.
Bṛhadāraṇyaka 3.7.23 describes the witness as the inner controller (antaryāmin): 'He who dwells in the mind, whom the mind does not know, whose body is the mind, who controls the mind from within — he is your ātman, the inner controller, the immortal.' Śaṅkara in his Vivekacūḍāmaṇi (verses 318–330) makes the sākṣī the centrepiece of his discrimination practice: the student is to recognise that the witness — pure awareness — cannot be the body (it observes the body), cannot be the mind (it observes the mind), cannot be the intellect (it observes the intellect), cannot be the ego (it observes the ego). What remains is the witness, which is Ātman, which is Brahman.
The philosophical problem of the witness in Advaita is its relationship to Brahman. If Brahman is non-dual and undivided, how can there be a witness distinct from what is witnessed? Śaṅkara's resolution: the distinction between witness and witnessed is itself within māyā — it is an appearance within consciousness, not a real metaphysical division. At the empirical level (vyāvahārika), there is a witness and there are objects witnessed. At the ultimate level (pāramārthika), witness and witnessed dissolve into the non-dual consciousness that Brahman is. The practice of recognising oneself as the witness is thus transitional — it moves the student from identifying as an object to identifying as the subject, and from there to recognising that the subject-object division itself arises within and does not exhaust Brahman.
Sources: Māṇḍūkya Upaniṣad 1.7; Bṛhadāraṇyaka Upaniṣad 3.7.23, trans. Swami Mādhavānanda (Advaita Ashrama, 2010); Śaṅkara, Vivekacūḍāmaṇi, trans. Swami Madhusudanasaraswati (Advaita Ashrama, 2009).