Dignaga was the founder of Buddhist logic and has been called the Father of Medieval Nyaya. He was an Indian Buddhist philosopher and logician who lived in the 5th and 6th centuries CE.

Contributions to Buddhist Logic:
Dignaga made significant contributions to the field of Buddhist logic. His work focused on the study of epistemology and perception, and he developed a system of logic known as the Pramanasamuccaya (Compendium of Valid Cognition). This work became the foundation of Buddhist logic and was highly influential in the development of Indian philosophy.

Key Concepts:
Dignaga's Pramanasamuccaya introduced several key concepts that were central to Buddhist logic:

1. Pramana: Dignaga classified knowledge into three types: perception (pratyaksha), inference (anumana), and verbal testimony (shabda). These three are considered the valid means of knowledge (pramanas) in Indian philosophy.

2. Hetu: Dignaga emphasized the role of inference in knowledge acquisition. He introduced the concept of hetu, which refers to the reason or evidence that supports a logical inference. According to Dignaga, a valid inference must have a hetu that is relevant and irrefutable.

3. Vyapti: Dignaga proposed the concept of vyapti, which is the universal relationship between a property (sadhya) and its defining characteristic (linga). Vyapti is the basis of logical reasoning and forms the foundation of inference.

Influence on Nyaya Philosophy:
Dignaga's contributions to Buddhist logic had a significant impact on the development of Nyaya philosophy. Nyaya, one of the six orthodox schools of Hindu philosophy, focuses on logic and epistemology. Dignaga's work provided a logical framework that influenced subsequent Nyaya thinkers, particularly during the medieval period.

Conclusion:
Dignaga's pioneering work in Buddhist logic established him as the founder of this field and earned him the title of the Father of Medieval Nyaya. His ideas on perception, inference, and valid cognition continue to be influential in the fields of Indian philosophy and logic.