The verse at Bṛh.U. III.8.8 is an interesting find. If only this section gave the ‘Imperishable’ (akṣaram) the attribute of possessing ‘nothing but knowledge’ (vijñāna-ghana), as we find earlier in Bṛh.U. II.4.12, to connect it well with the sections in DN.11 & MN. 49 of the Nikāyas.
In Bṛh.U. II.4.12 the Self is considered as a great being consisting of nothing but knowledge (evaṃ vā ara idaṃ mahad bhūtam anatam apāraṃ vijñāna-ghana), and is immersed into the corporeal and permeates it as were a lump of salt into water. With the departing of Self, so departs knowledge.
Two verses later (II.4.14), this is explained, that ‘where there is duality’ (yatra hi dvaitram iva bhavati): one smells another, sees another, hears another, speaks to another, thinks of another, understands another…although where everything has become unified with Self (sarvam ātmaivābhūt), the question is asked ‘by what and whom should one smell … ect. … whereas the Ātman is then indicated as the knower of all that is known:
- “By what should one know that by which all this is known? By what, my dear, should one know the knower?”
“…yenedam sarvaṃ vijānāti, taṃ kena vijānīyāt, vijñātāram are kena vijānīyād iti.” (Bṛh.U. II.4.14)
Although these are separate exchanges of dialogue, Bṛh.U. II.4 & III.8., the context is still the dynamic of Ātman, immersed in the corporeal but not touched by it, attributes notwithstanding. We know that the Tathāgata used the manner of philosophical exchange in his day, and in some cases made direct puns on contemporary doctrinal idiom. This may well be one of those. But as you say, ‘Certainly not enough out of which to make a mountain of dogma, but intriguing nonetheless.’ Even still, I’ll bookmark it for later.
I did notice later in the section you cited, Bṛh.U. III.8.11, another Upaniṣadic idiom that the Tathāgata punched at some. That is dṛṣṭe, śrute, mate, vijñāte, that I mentioned after the earlier comment on Vaccagotta here. This came up at least twice that I know of in the Nikāyas at MN.22 and AN.4.24. What makes this occurrence interesting is that this verse says that the ‘Imperishable’ (akṣaram):
- “…is unseen but is the seer, is unheard but is the hearer, unthought but is the thinker, unknown but is the knower. There is no other seer but this, there is no other hearer but this, there is no other thinker but this, there is no other knower but this.”
…tad vā etad akṣaraṃ gārgy adṛṣṭaṃ draṣṭṛ, aśrutaṃ śrotṛ, amataṃ mantṛ, avijñātaṃ vijñātṛ, nānyad ato 'sti draṣṭṛ, nānyad ato 'sti śrotṛ, nānyad ato 'sti mantṛ,nānyad ato 'sti vijñātṛ
- “Thus it is, bhikkhus, when the Tathāgata sees what is to be seen; he does not imagine the seen, does not imagine the not-seen, does not imagine what is to be seen, and does not imagine a seer. When hearing what is to be heard; does not imagine the heard, does not imagine the not-heard, does not imagine what is to be heard, and does not imagine a hearer. When thinking what is to be thought; does not imagine the thought, does not imagine the not-thought, does not imagine what is to be thought, and does not imagine a thinker. When cognizing what is to be cognized; does not imagine the cognized, does not imagine the not-cognized, does not imagine what is to be cognized, and does not imagine a cognizer.
Iti kho, bhikkhave, tathāgato daṭṭhā daṭṭhabbaṃ, diṭṭhaṃ na maññati, adiṭṭhaṃ na maññati, daṭṭhabbaṃ na maññati, daṭṭhāraṃ na maññati; sutvā sotabbaṃ, sutaṃ na maññati, asutaṃ na maññati, sotabbaṃ na maññati, sotāraṃ na maññati; mutvā motabbaṃ, mutaṃ na maññati, amutaṃ na maññati, motabbaṃ na maññati, motāraṃ na maññati; viññatvā viññātabbaṃ, viññātaṃ na maññati, aviññātaṃ na maññati, viññātabbaṃ na maññati, viññātāraṃ na maññati.