asa~Nga is most probably the first Buddhist AchArya to establish vij~nAnavAda on the basis of tarka. He was the first Buddhist philosopher to introduce the pa~nchAvayavI parArthAnumAna of the naiyAyika-s into the field of study of vij~nAnavAda. He is also the source of numerous axioms of vAdakalA used till the current day by Buddhist theologians. These axioms or rules are similar to those of gautama popular within the school of nyAya. Though maitreya had already discussed vAdakalA in his work saptadasha bhUmishAstra, asa~Nga’s handling of this topic far exceeds that of his guru both in terms of depth and detail.
Arya asa~Nga took birth in gAndhAra in 450 A.D. Initially he was an adherent of the vaibhAshika sampradAya but later turned to vij~nAnavAda after coming in contact with AchArya maitreya. asa~Nga was the elder brother of vasubandhu, known as the second Buddha in Buddhist circles. The greatest contribution of asa~Nga is his bauddha nyAya or pramANa-shAstra, which is available to us today in the seventh and sixteenth chapters of mahAyAnAbhidharma-saMyukta-sa~NgitishAstra. His thoughts on nyAya however do not contradict those of maitreya.
asa~Nga accepts four pramANas: pratyakSha, anumAna, upamAna and Agama. As an a~Nga of anumAna, he also accepts pratij~nA and other avayavas. Thus, the influence of prAchIna gautamIya nyAya on asa~Nga is distinctly evident.
Vasubandhu was initially a sarvAstivAdin and later turned to vijnAnavAda under the influence of his brother asanga. Vasubandhu’s contribution to the school of vjnAnavAda is incomparable. This statement can be even expanded to include entire Buddhism. The vaibhAShika school finds itself frequently expressing gratitude ot vasubandhu as well. Of the thirty-two written works of vasubandhu available today, three are of importance from the standpoint of nyAya.
While these three works do not seem to have been translated to Tibetan, incomplete Chinese translations of vAda-vidhi are available scattered across Asia. From a close examination of the available portion of this work, a striking similarity to gautamIya nyAya becomes clear. It is known that Hiuen Tsang gathered these three works during his visit to India. Apart from these three works, a Chinese translation of another work named tarka-shAstra is also available. This work constitutes of three chapters, the first one dealing with a commentary of the panchAvayava-s. The second chapter deals with jAti or asaduttara and the third with the twenty-two nigraha-sthAnas. This indicates another important aspect, the influence of vAtsyAyana on vasubandhu. According to vasubandhu, there needs to be a prayoga of panchAvayava-s in vAda, two for bodha (which are pratij~nA and hetu).
There is also a notion that vAda-vidhi is a part of the larger work tarka-shAstra.
In the arena of bauddha nyAya, di~NnAga is second only to vasubandhu. Even with the expansive flourishing of the four schools of Buddhism, bauddha nyAya saw little development till about fourth century. Though nAgArjuna authored an independent work on nyAya in the third century, it was merely an examination of gautamIya nyAya siddhAnta. The concepts of nyAya popularized by maitreya, asanga and vasubandhu were not only based on vijnAnavAda but borrowed heavily from vaibhAShika siddhAnta as well. The credit of establishing bauddha nyAya on the canvas of pure vijnAnavAda goes undoubtedly to di~NnAga. His key contribution was to separate nyAya from darshana and dharma and establish it as an independent branch of knowledge.
The time of di~NnAga is established to be around fifth century. It is also believed that di~NnAga was a disciple of vasubandhu and belonged to Southern India. It can be guessed that he received instruction into bauddha dharma from some vAtsIputrIya AchArya. Owing to several disagreements with his guru, he migrated to Magadha for instruction. Those were the times when vasubandhu was known throughout India as pratibuddha.
Di~NnAga challenged various philosophers to debates during his travels in Nalanda, Odissa and Maharashtra. He even expressed disagreement with his own guru vasubandhu at times. Not only does he face criticism from udyotakarAchArya, vAchaspati and other Astika naiyAyikas, but also from several jaina tArkikas. His disciple and commentator dharmakIrti is critical of his guru at places as well.
All written works of di~NnAga re possibly related to nyAya. His independent works on nyAya include pramANa samucchaya, nyAyapravesha, AlamvanaparIkShA, hetuchakra samarthana, nyAyamukha, Alamvana parIkShAvrtti and trijAla parIkShA. Of these, pramANa samucchaya is the pathapradarshaka grantha of bauddha nyAya. Various smaller essays of di~NnAga are available in Chinese and Tibetan languages today. He himself later collected these essays with extensive notes in six volumes: pratyakSha, sarvArthanumAna, parArthanumAna, hetudrShTAnta, apoha and jAti. A commentary on these by jinendra buddhi is available currently.
Di~NnAga rejects the panchAvayava-s of gautamIya naiyAyikas and accepts only three – pratijnA, hetu and udAharaNa as angas of anumAna. The critique of the lakShaNa of pratyakSha and anumAna - as expounded by gautama and vAtsyAyana - by di~NnAga is so emphatic and extensive that udyotakarAchArya has authored an entire vArtika for the khaNDana of the siddhAnta-s of di~NnAga. shrI kumArila bhaTTapAda extensively refutes the theories of di~NnAga in his shloka-vArtika.
dharmakIrti took birth in Southern India in a brAhmaNa household at the sacred tirumalai kShetra. He studied the vaidika shAstras according to his family tradition. He was later initiated into bauddha mata and studied under a direct disciple of vasubandhu at Nalanda. It is known that he studied under a Buddhist named Ishvarasena. jayanta bhaTTa, who is critical of dharmakIrti does not fail to describe him as sunipuNabuddhi and jagadabhibhavadhIra.
While the chief topic of all of dharmakIrti’s works is nyAya, one can see in them the converge of various Buddhist concepts, especially of vijnAnavAda. Though the chief structure of his works is in the form of commentary to dignAga’s writings, dharmakIrti gives a new dimension to dignAga’s thoughts. Among his seven works, pramANavArtika is of primary importance. In this work, he analyses both prameya and pramANa of bauddha nyAya. pramANa-vinishchaya is yet another work of dharmakIrti dealing with pramANa and consists of 1340 verses. His other works, most of which are only available in Tibetan language, are: nyAyabindu, hetubindu, vAdanyAya, sambandhaparIkShA, santAnAntarasiddhi etc. There have been several commentaries written on dharmakIrti’s works. Again, these seem to be available only in Tibetan translations.
After dharmakIrti, shAntarakshita, kamalashIla, dharmottara, jnAnashrI and other tArkikas continued contributing towards bauddha nyAya. But after the period of dharmakIrti, the glory of not only bauddha nyAya, but also of bauddha dharma began to dwindle and in no uncertain terms.