Abstract
Nyāya, which is one of the orthodox Brahmanical schools in India, accepts the authority of both the Vedic scriptures and God as its composer. Nyāya has specialized in logic and argumentation from ancient times while at the same time gradually strengthening its theistic tendency. Nyāya polemicist, Udayana, is famous for his contribution to the rational proof of the existence of God. In this paper, I will consider a tiny part of his proof of the existence of God given in his theistic monograph, the Nyāyakusumāñjali, and in particular a topic called prāmāṇyavāda, or the Theory of Validity, from the viewpoint of the historical development of this argument. In this topic, it is argued how we justify our cognition and undertake actions. Nyāya polemicists preceding Udayana argued this topic in order to justify the Vedic scriptures and to encourage people to perform the Vedic rituals. And this topic has had little relationship with theological context. However, Udayana seems to link this argument to his theory of theology in an implicit way. I will suppose in his argument the implicit linkage between the prāmāṇyavāda and the assumption of an omniscient being.