Wikipedia
Ratnakīrti (11th century CE) was a Buddhist philosopher of the Yogacara and epistemological schools (pramanavada) who wrote on logic, philosophy of mind and epistemology. Ratnakīrti studied at Vikramashila university under Jñanasrimitra (975–1025).
Ratnakīrti's 'Refutation of Other mindstreams' (Saṃtãnãntaradusana), argued that knowledge of external streams of consciousness ( citta-santāna) is a form of inference (anumāna), not a direct perception (pratyakṣa). Ratnakīrti introduced the two truths doctrine as key to the nature of the discussion. Since inference deals with conceptual universals, the proof of the mindstreams of others, whilst empirically valid in relative truth (saṃvṛtisatya), does not hold ultimate metaphysical certainty in absolute truth (paramārthasatya). Ratnakīrti therefore argued for the ultimate truth of "one mind" (ekacitta). By establishing the impossibility of external mindstreams, Ratnakīrti was also arguing for the non-dualism of Yogacara "consciousness-only". Ratnakīrti argued that from an ultimate point of view, the distinctions between a subject and object, the observer and the observed, all disappear. Ratnakīrti's theory states then, that there is no logical foundation for individuating mindstreams, and that there are no boundaries between minds from the perspective of ultimate truth. This sub school of Yogacara Cittamatra (mind only) has been called the Citradvaitavada school (non-dual mind) or Vijñanadvaitavada school (non-dual consciousness).
Ratnakīrti's "Refutation of Arguments Establishing Īśvara" (Īśvara-sādhana-dūṣaṇa) argued against the Hindu concept of a creator God.
Ratnakīrti also wrote the "Proof of Momentariness" (Kṣānabhaṅgasiddhi), where he defended the theory of momentariness, the view that dharmas last only for a moment.