(from B.S.B. II,i.11)
For this further reason, one should not on the strength of mere logic challenge something that has to be known from the Vedas. For reasoning that has no Vedic foundation and springs from the mere imagination of persons, lacks conclusiveness. For man’s conjecture has no limits. Thus it is seen that an argument discovered by adepts with great effort is falsified by other adepts; and an argument hit upon by the latter is proved to be hollow by still others. So nobody can rely on any argument as conclusive, for human intellect differs.
What are the things that have to be learned from the Vedas according to Sankara?
Although reasoning may be noticed to have finality in some contexts, still in the present context it cannot possibly get any immunity from the charge of being inconclusive; for this extremely sublime subject-matter, concerned with the reality of the cause of the Universe and leading to the goal of liberation, cannot even be guessed without the help of the Vedas. And we have said that It cannot be known either through perception, being devoid of form, etc, or through inference etc., being devoid of the grounds of inference etc.
Now the question arises: is the non-demonstrability of the existence of God/Brahman a matter for rational discourse or not? Sankara continues with his depreciation of reason as a means to firm knowledge in this regard.
For it is a patent fact of experience, that when a logician asserts, “This indeed is the true knowledge”, it is upset by someone else. And what is established by the latter is disproved by still another. How can any knowledge, arising from reasoning, be correct when its content has no fixity of form?
Real adepts will have noticed that I have by careful selection established a specious argument for leaving out Sankara from philosophical study much as Bertrand Russel got away with giving a mere 13 pages to Thomas Aquinas in what has been called ‘a monument to one man’s prejudice, his History of Western Philosophy. You can extract a rationale for this by the following from his work: (from Aquinas on Faith: faith)
Insofar as it conveys vision, cognition is distinguished from faith. This is why Gregory says that things that are seen have cognition rather than faith. According to Augustine in On Seeing God, those things are said to be seen which are present to the senses or to the intellect. But things that are said to be present to the intellect do not exceed its capacity.
However, as far as the certitude of the assent is concerned, faith is a cognition, a cognition by virtue of which it can be called a knowledge and a vision, according to 1 Corinthians 13:12: "We see now darkly through a mirror." And this is what Augustine says in On Seeing God: "If it is not improper to say that we know that which we believe most certainly, then from this it follows that we are rightly said to see with the mind the things that are believed, even though they are not present to our senses."
Selective extracts of both Sankara and Aquinas can cause both to be relegated to exterior darkness when in fact a comprehensive study reveals close reasoning of the highest order.