Masaaki explains the doctrine thus: a word indicates an object merely through the exclusion of other objects (anyapoha, -vyavrtti). For example, the word "cow" simply means that the object is not a non-cow. As such, a word cannot denote anything real, whether it be an individual (vyakti), a universal (jati), or any other thing. The apprehension of an object by means of the exclusion of other objects is nothing but an inference. Works As noted by Hayes, the difficulty in studying the highly terse works of Dignāga is considerable, because none of them have survived in the original Sanskrit and the Tibetan and Chinese translations which do survive show signs of having been done by translators who were not completely certain of the meaning of the work. This difficulty has also led scholars to read Dignaga through the lens of later authors such as Dharmakirti and their Indian and Tibetan interpreters as well as their Hindu Nyaya opponents. Because of this tendency in scholarship, ideas which are actually innovations of Dharmakirti and later authors have often been associated with Dignaga by scholars such as Fyodor Shcherbatskoy and S. Mookerjee, even though these thinkers often differ. Dignāga's magnum opus, the Pramāṇa-samuccaya (Compendium of Valid Cognition), examined perception, language and inferential reasoning. It presents perception as a bare cognition, devoid of conceptualization and sees language as useful fictions created through a process of exclusion (Apoha). Other works include: Hetucakra (The wheel of reason), considered his first work on formal logic. It may be regarded as a bridge between the older doctrine of trairūpya and Dignāga's own later theory of vyapti which is a concept related to the Western notion of implication. Alambana-parīkṣā, (The Treatise on the Objects of Cognition) and its auto commentary (vrtti). Abhidharmakośa-marma-pradīpa – a condensed summary of Vasubandhu's seminal work the Abhidharmakosha A summary of the Mahayana Aṣṭasāhasrika-prajñāpāramitā sūtra Trikāla-parikṣa, (Treatise on the tri-temporality) Nyāya-mukha (Introduction to logic). Tradition and influence Dignāga founded a tradition of Buddhist epistemology and reasoning, and this school is sometimes called the "School of Dignāga" or "The school of Dinnāga and Dharmakīrti" (due to the strong influence of Dharmakīrti as well). In Tibetan it is often called “those who follow reasoning” (Tibetan: rigs pa rjes su ‘brang ba); in modern literature it is sometimes known by the Sanskrit 'pramāṇavāda', often translated as "the Epistemological School." Many of the figures in these were commentators on