Buddhist logico-epistemology is a term used in Western scholarship for pramāṇa-vāda (doctrine of proof) and Hetu-vidya (science of causes). Pramāṇa-vāda is an epistemological study of the nature of knowledge; Hetu-vidya is a system of logic. These models developed in India during the 5th through 7th centuries. The first Buddhist thinker to discuss logical and epistemic issues systematically was Vasubandhu in his Vāda-vidhi ("A Method for Argumentation"), who was influenced by the Hindu work on reasoning, the Nyāya-sūtra.