Udayana c. 975 – c. 1050

Udayana was an Indian philosopher of the eleventh century, the most important figure of the late Nyaya tradition before the rise of Navya-Nyaya, who systematized the union of Nyaya logic and Vaiseshika ontology in his treatises Nyaya-kusumanjali and Atma-tattva-viveka. The Nyaya-kusumanjali, A Handful of Flowers of Logic, mounted a sustained set of arguments for the existence of God on the basis of reasons drawn from causality, design, the power of words, and the moral structure of the world, in conscious response to the criticisms of the Buddhist logical tradition. His critique of Buddhist no-self doctrine in Atma-tattva-viveka shaped the orthodox Hindu reply for centuries.

Udayanācārya, conventionally Udayana, flourished in Mithila in northern India around the late tenth and early eleventh centuries. The traditional dates set him between about 975 and 1050; he wrote in Sanskrit, was regarded as a śāstrin of the highest distinction in his own day, and was honoured by tradition as the philosopher who had finally answered the Buddhist critique of Brahmanical thought.

His major works are the Kiraṇāvalī, a sustained commentary on Praśastapāda's Padārthadharmasaṃgraha; the Lakṣaṇāvalī, a brief manual of Vaiśeṣika definitions; the Nyāyavārttikatātparyapariśuddhi, a refinement of the earlier Nyāya commentaries; the Ātmatattvaviveka, a long defence of the existence of the self against the Buddhist doctrine of momentariness and not-self; and the celebrated Nyāyakusumāñjali (Bouquet of Argument-Flowers), five-chapter manual of natural theology.

Udayana brought together the older logical-epistemological tradition of Nyāya with the categorial ontology of Vaiśeṣika into the synthetic Nyāya-Vaiśeṣika that became classical Indian theism's principal philosophical discipline. The Nyāyakusumāñjali assembled the cosmological, design, moral, and authority arguments for the existence of God in a form on which centuries of Indian theistic philosophy depended; and his work prepared the ground for Gaṅgeśa's foundation of Navya-Nyāya around 1300.