Dignāga

Dignāga (c. 480 – c. 540 CE) was an Indian Buddhist scholar and one of the Buddhist founders of Indian logic (hetu vidyā). Dignāga's work laid the groundwork for the development of deductive logic in India and created the first system of Buddhist logic and epistemology (Pramana). According to Georges B Dreyfus, his philosophical school brought about an Indian "epistemological turn" and became the "standard formulation of Buddhist logic and epistemology in India and Tibet." Dignāga's thought influenced later Buddhist philosophers like Dharmakirti and also Hindu thinkers of the Nyaya school. Dignāga's epistemology accepted only "perception" (pratyaksa) and "inference" (anumāṇa) are valid instruments of knowledge.
Dignāga was born into a South Indian Brahmin family in Simhavakta near Kanchipuram and very little is known of his early years, except that he took as his spiritual preceptor Nagadatta of the Pudgalavada school before being expelled and becoming a student of Vasubandhu.

Buddhist epistemology holds that perception and inference are the means to correct knowledge.

Dignāga's epistemology holds that there are only two 'instruments of knowledge' or 'valid cognitions' (pramāṇa); "perception" (pratyaksa) and "inference" (anumāṇa). Perception is a non-conceptual knowing of particulars which is bound by causality, while inference is reasonable, linguistic and conceptual. This conservative epistemic theory was in contrast to the Nyaya school who accepted other means of knowledge such as Upamāṇa (comparison and analogy).

During Dignāga's time, the Nyaya school of Hinduism had begun to hold debates using their five-step approach to making and evaluating arguments with logic. Buddhist debaters such as Dignāga wanted to engage in these debates, and also have a way to logically evaluate arguments, but a premise such as "all dogs are mammals" proved problematic for his idealist Yogacara philosophy. Dignāga was a student of Vasubandhu, and therefore believed that "dharmas are empty." In other words, there are not universal qualities such as "dog-ness" or "mammal-ness." Such universals would have to be unchanging, and since all things are subject to change and are lacking in essential essence according to his school of philosophy, Dignāga attempted to find a way to engage in argument within the Nyaya school without positing metaphysical Universals.

To do this he employed what is referred to in formal logic in the West as contraposition, or in Sanskrit, Apoha, where one switches the terms and swaps them for their term complement. Therefore, the example premise above, "all dogs are mammals" becomes "all non-mammals are non-dogs." These two statements are logically equivalent. Once this had been done, Dignāga could make arguments about non-mammals without explicitly positing that mammals have an essential nature. While this move gets off the ground towards his goal, reflection shows that making universal statements about non-mammals still implies that there are mammals who share an essential nature, and everything else, which lacks this "mammal-ness." Still, using this method Dignāga and other Buddhist logicians were able to further their logical discourse and felt more comfortable engaging in Nyaya structured debates.

Among Dignāga's works there is Hetucakra (The wheel of reason), considered his first work on formal logic, advancing a new form of deductive reasoning. It may be regarded as a bridge between the older doctrine of trairūpya and Dignāga's own later theory of vyapti which is a concept related to the Western notion of implication.

Dignāga's most important work, the Pramāṇa-samuccaya (Compendium of Valid Cognition), examined perception, language and inferential reasoning. It presents perception as a bare cognition, devoid of conceptualization and sees language as useful fictions created through a process of exclusion (Apoha).

Other works include:

• Alambana-parīkṣā, (The Treatise on the Objects of Cognition)
• Abhidharmakośa-marma-pradīpa – a condensed summary of Vasubandhu's seminal work
• A summary of the Aṣṭasāhasrika-prajñāpāramitā sūtra
• Trikāla-parikṣa
• Nyāya-mukha

Dignāga founded a tradition of Buddhist logic, and this school is sometimes called the "School of Dignāga" or the "Dignāga-Dharmakīrti school". In Tibetan it is often called “those who follow reasoning” (Tibetan: rigs pa rjes su ‘brang ba); in modern literature it is sometimes known by the Sanskrit 'pramāṇavāda', often translated as "the Epistemological School" or "The logico-epistemological school."

Buddhist philosophers who wrote on pramana include:

• Dharmakīrti (c. 7th century)
• Jinendrabuddhi
• Dharmapala of Nalanda
• Santabhadra
• Śāntarakṣita (725–788)
• Dharmottara (8th century)
• Prajñakaragupta
• Samkarananda
• Ratnākaraśānti (c.1000)
• Jñanasrimitra (975–1025)
• Ratnakīrti (11th century)

This tradition of logic and epistemology continued in Tibet, where it was expanded by thinkers such as Cha-ba (1182–1251) and Sakya Pandita (1182–1251).

Dignaga also influenced non-Buddhist Sanskrit thinkers. According to Lawrence J. McCrea, and Parimal G. Patil, Dignaga set in motion an "epistemic turn" in Indian philosophy:

In the centuries following Dignāga’s work, virtually all philosophical questions were reconfigured as epistemological ones. That is, when making any claim at all, it came to be seen as incumbent on a philosopher to situate that claim within a fully developed theory of knowledge. The systematic articulation and interrogation of the underlying presuppositions of all knowledge claims thus became the central preoccupation of most Sanskrit philosophers."