It is sometimes said that Advaita Vedanta began with Gaudapada’s commentary on the Mandukya Upanishad.
It is from this Upanishad and commentary that we get the doctrine of the three states (waking, dream, and sleep) and turiya, the fourth.
Whether Advaita really began with Gaudapada’s commentary, I don’t know. I’m not an intellectual historian. But there’s no doubt that this text played a crucial role in Advaita’s evolution.
Adi Shankara, the most important Advaitin philosopher, said that this Upanishad and commentary contain “the quintessence of the substance of the entire philosophy of Vedanta.”
Gaudapada was the teacher of Shankara’s teacher.
In his commentary on Gaudapada’s commentary, Shankara wrote:
(Objection)—Consciousness is seen to change (disappear) in deep sleep.
(Reply)—No, the state of deep sleep is a matter of experience. For the Śruti says, “Knowledge of the Knower is never absent.”
Much of Shankara’s writing is in this form of an imaginary debate. The reply states Shankara’s views.
Let’s hear Shankara’s opinion again:
The state of deep sleep is a matter of experience. For the Śruti says, “Knowledge of the Knower is never absent.”
We can all testify from experience, at least potentially, that the first sentence is true. I’ll explain why I say this in a moment.
But I’ve also experienced something else that had never yet happened to anyone on earth when Shankara wrote those words in the 9th century: general anesthesia in an operating room. One moment I was counting backwards from ten, like the anesthesiologist told me, and the next moment I was in the recovery room. According to the clock several hours had passed, but there was no experience of it.
Deep sleep and general anesthesia are very different. The reason I said we can all potentially testify that we are conscious during sleep is because once you’ve had general anesthesia — at least general anesthesia with the drugs used on me — you can see by comparison that you are conscious during sleep. If you don’t believe me, call your friendly neighborhood anesthesiologist and give it a whirl.
(Objection)—Freddie, you were conscious while anesthetized but your memory was disabled by the drug so you don’t remember.
(Reply)—Maybe, but how can you prove that?
If I wasn’t conscious during those hours — and I don’t believe I was — then it’s not true as a matter of experience that “Knowledge of the Knower is never absent.”
That Knowing Knower is Brahman.
I wonder, if general anesthesia had existed in 9th century India and Shankara had received it, would Advaita Vedanta be different?
The Maharaja of Mysore mentioned in the foreword of the book linked below, Sri Krishnaraja Wadiyar Bahadur IV, is the same Maharaja whose prime minister hired Maurice Frydman, the co-author of I Am That, and brought him to India.
Jan Esmann says in his second BatGap interview at 37:57 that he was conscious while under general anesthesia.