We do not really know exactly when Shankara and Guadapada lived and died
- it's mostly speculation. There isn't even any historical proof that
Shankara founded four monasteries in the first place. All we have is
some manuscripts that were preserved and an oral tradition. We do know
that Shankara quoted Chandrakiriti, the famous Buddhist logician.
The distinctions between Advaita and Vajrayana are just too subtle for
most causal readers. That's about all I can say at this point. Perhaps
if you get time you can explain it in more detail. Apparently both
Gaudpada and Shankara were cryoto-Buddhists: Nirvana is Brahman, /the
pure non-dual consciousness./ There may be some finer details to
consider, but this is the main gist of the doctrine.
The only doctrine to discuss would be the nature of /maya/ as propounded
by the Adi Shankara. There is just no reason I can determine that would
justify a presupposition that Brahman is the ultimate reality, since it
isn't an a priori notion, but everyone can experience the nature of
/Pure Consciousness,/ call it what you will.
There is just nothing in the Vedic literature that would suggest the
doctrine of non-dualism previous to Gaudapada. Madhva, Ramanuja,
Vallabha, Nimbarka and Chaitanya all agree on this - all were dualists
or quasi dualists. All of the Upanishads were composed after the
historical Buddha's passing. And all of the Upanishadic thinkers were
transcendentalists. Apparently Gaudapda adopted the Buddhist doctrines
that /ultimate reality is pure consciousness/ and that the nature of the
world is the four-cornered negation. Gaudapada adapted both doctrines
into a philosophy of the Mandukaya Upanisad Karika, which was further
developed by Shankara. The Vajrayana similarities are unmistakable,
according to Raju and Sharma.
Compare:
Excerpt from /mANDUkya kArikA IV by gauDapAda:/
"Duality is only an appearance; non-duality is
the real truth. The object exists as an object
for the knowing subject; but it does not exist
outside of consciousness because the distinction
of subject and object is within consciousness."
Excerpt from /vijnApti matratA siddhi by vasAabAndhu: /
"Reality is Pure Consciousness; external objects
do not exist outside thought. Reality can be
directly realized by transcending the
subject-object duality." - vimshAtika-Vrtti on kArikA
Work cited:
Raju 1992, Raju, P.T., /The Philosophical Traditions of India/, Motilal
Banarsidass, p. 177.
Sharma, Chandrahar, /A Critical Survey of Indian Philosophy/, Rider, p.
245-246.
