Pramanas as irreducible means of knowledge

An important and to my mind a very interesting aspect of the Pramana (Means of Valid Knowledge) theory is that each pramana is unique and cannot be reduced to any other. Dharmaraja Adhvarindra writer of the classic book on the topic Vedanta Paribhasa which he says is for the enlightenment of backward students is at great pains to stress this point particularly on the pramanas which are not universally recognised as separate by all schools. He recognised 6 whereas Vaisesika counted 2, Sankhya 3, and Nyaya 4. He justifies the inclusion of upamana (Comparison) and anupalabadhi (Non-Apprehension of Existence) as freestanding which other schools reduced to a function of pratyaksha (Perception).


This point is not mentioned in the Wikipedia article on the pramanas, unless I missed it. I also sense that this ‘gavaya in the room’ is overlooked generally but I could be wrong by those who would link upamana to modality. While on the topic of modality surely the ultimate source of deontic modadlity is the Gita - what ought I do, what can I do, what may I do, what must one do and what is impossible.