Uddalaka’s distinguished disciple Yājñavalkya, in the Bṛhadāraṇyaka Upaniṣad, lays out a simple algorithmic rule to get to Brahman, to ‘That’.
The exact word used is Ātman, a synonymous appellation and related to the English word ‘Animate’: to come alive, [the Latin Anima Mundi]. Ātman is simply: ‘That which animates Life’.
As is uniformly true of all radically revealing insights it was ridiculously simple to lay-out [and not so simple to effect]. The formula is: ‘It is not this! It is not this!’ [Neti, Neti].
The common interpretation is that this was a sweeping rejection of ‘World as Object’ and a relapse to an ‘Inner Self’ in line with the terminus of the Chandogya Upanishad.
The Rule has two parts: ‘It is not this!’ directed at Objects in an effecting of the Principle of Co-Dependence. Second, the turn-around to the Subject. The act of Self-Scuttle: ‘It is not this!’; It is not: ‘It is not this!’
The complete rule properly interpreted is a self-scuttling circular loop. But if limited to a a linear and lateral unfolding Yājñavalkya’s Rule has no natural convergence and will enter into an insidious spin. And the reel will spin forever if you don’t at some point see that you are part of the movie.
No amount of negating will lead to convergence unless the negating finally turns in on itself. The formula completes, the circle is rounded only when the aim, act and agent of negation are themselves consumed in full self-scuttle.
A meta-statement is an assertion about an assertion. Yājñavalkya’s Rule, properly rounded becomes: ‘It is not this! It is not: ‘It is not this!’
When properly rounded Yājñavalkya’s Rule would have been the first formulated Self-Negating Expression. And the earliest definition for the Symbol ‘0’.
Yājñavalkya himself could never have heard of the word Shūnyam or shown any recognition of the Symbol ‘0’ as we know it. They did not take shape for another 500 plus years at the earliest.
‘Brahman‘ is a very slippery term and unless you are acutely aware of the Self-Loop resident at it’s center you will assuredly get lost. And there is no end to the literature following Yājñavalkya that does precisely that.
Did Yājñavalkya himself round the Rule? I don’t know. There are lines and verses that can be cited to prove either result. And we will never know how many of them were Teachings accommodated to ‘Skillful Means’. But then these texts are 3,000 years old. Holding one’s tongue is not a misplaced virtue.
A great deal originates with the pioneering Yājñavalkya, including the intuition for the Axioms of Sight, the most compact definition of ‘Not-Two’ [Àdvaitham] and the plain talk about: ‘The Other Shore’.
Two thousand years later variants of the Rule rebirth in world philosophies as the ‘Via Negativa‘, Coincidentia Oppositorum, Docta Ignoranta and so on.