Along with refining rules for differentiating sound arguments from various sorts of fallacies, he also made important contributions to Buddhist epistemology. He defined perception as 'devoid of conceptual constructions' (kalpanâpoḍha 無分別), such as memory, desires, doubts, hallucinations, mirages, etc. 「由此即說。憶念, 比度,悕求, 疑智, 惑亂智等,於麤愛等,皆非現量。」 〔Nyāyamukha, T 1628.32.3b26–7〕 ). Distinguishing perceptual knowledge (pratyakṣa-pramāṇa) into three factors: (1) the instrument causing perceptual cognition (pramāṇa 量), (2) the perception that results (pramāṇa-phala 量果), and (3) the sense that the perception is being experienced as oneʼs own (svasaṃvitti 自證)—he insisted that that differentiation is only a figurative distinction (upacāra 假說) for the resultant cognition (pramāṇa-phala) 「又於貪等諸自證分。諸修定者離教分別皆是現量。於此中無別量果。以即此體似義生故。有用故假說為量。於貪等諸自證分亦是現量。何故此中除分別智。遮此中自證。現量無分別故。」 (Nyāyamukha T 1628.32.3b21–25; cf. Pramāṇasamuccaya 1.8–10). For more detail on Dignāgaʼs system, see under 能立.

Dignāgaʼs Life: As with many figures from this period of Indian history, accurate historical details are few, and what the Buddhist tradition relays is shrouded in myth and hagiography. He was a native of South India. According to Tibetan tradition he was from Kañci (associated a generation or two later with Dharmapāla 護法), and originally was an adherent of the Vātsīputrīya 有犢子部 (Pudgala-vāda) school. However, Chinese tradition places him near the capital of Andhra 案達羅國, Veṅgīpura 瓶耆羅. Xuanzang 玄奘 mentions visiting a stone stūpa on the peak of a desolate hill a little over twenty li from Veṅgīpura where Dignāga composed his hetu-vidyā treatises. (孤山。山嶺有石窣堵波。陳那(唐言授)菩薩於此作因明論。 Xiyuji 西域記, T 2087.51.930b12–14; cf. Datang Ci'ensi sanzang fashi zhuan 大唐大慈恩寺三藏法師傳T 2053.50.241b15). Xuanzang makes no mention of any connection to Vātsīputrīyas; instead he offers a legend of how Mañjuśrī 妙吉祥菩薩 convinced Dignāga to propagate Maitreyaʼs Yogâcārabhūmi-śāstra (慈氏菩薩所製瑜伽師地論; Xiyuji, T 2087.51.930c4). In response Dignāga first wrote the logic treatises to make hetu-vidyā accessible, and then devoted himself to promoting the Yogâcārabhūmi (Xiyuji T 2087.51.930c8).

While the Chinese tradition (including Yijing 義淨, who translated Dignāga works into Chinese, but was not himself a Yogâcāra) considers Dignāga part of the Yogâcāra tradition 瑜伽行派, the Tibetan tradition and, in turn, modern scholars, have long debated whether to consider Dignāga a Yogâcāra or a Sautrāntika 經量部, or whether he might have transitioned from one to the other across different works. Since Bhāviveka 淸辯 (Madhyamaka-hṛdaya-kārikāḥ with Tarkajvālā, ch. 5), Candrakīrti (Madhyamakâvatāra , ch. 6), etc., attack Dignāga as a prime representative of the Yogâcāra school; the Chinese tradition unambiguously places him in the Yogâcāra tradition; and the Tibetan sources are from many centuries after the fact, the Indian and Chinese opinion on Dignāgaʼs affiliation should be taken as authoritative. The debate on whether to consider Dignāga a Sautrāntika or Yogâcāra usually amounts to trying to determine whether he accepted or rejected the existence of 'external objects (bāhyârtha, 外義).' This debate, too, should be moot, since the penultimate sentence of his Ālambana-parīkṣā 觀所緣緣論—in which he demonstrates that atomic theory is incapable of explaining what cognitive objects rely on (ālambana 所緣)—states:

As to whether the two rūpas—viz. indriya and viṣaya—and consciousness are the same or different, or whether they are neither the same nor different: One can say according to oneʼs wishes (隨樂, yathā-āśaya). 根境二色與識一異或非一異。隨樂應說。(Xuanzangʼs translation, T 1624.31.889a9) 1

In short, Dignāgaʼs position was agnostic on the status of external objects, so that if we force an interpretation on him that insists his position or motives lean one way or the other, we are thinking about something other than what he thought he had accomplished by refuting atomic theories.

Dignāgaʼs Works:

1. His major work, Pramāṇasamuccaya 集量論, preserved in two problematic Tibetan translations, is not available in Sanskrit and was never translated into Chinese (except for a short excerpt translated by Xuanzang in the Cheng weishilun, T 1585.31.10b14–16). M. Hattori has translated the first chapter from the Tibetan: Dignāga, On Perception, Cambridge, MA: Harvard University Press, 1968. Recently recovered Sanskrit mss. of Jinendrabuddhiʼs commentary are being edited and published by E. Steinkellner, et al.
2. His Nyāyamukha 因明正理門論 survives only in Chinese translations: (1) T 1628, translated by Xuanzang in 650; (2) T 1629, translated by Yijing in 711. G. Tucci published an English translation, The Nyāyamukha of Dignāga, Leipzig and Heidelberg: Otto Harrassowitz, 1930.
3. Ālambana-parīkṣā (extant only in Chinese and Tibetan). (1) 無相思塵論, T 1619.31, translated by Paramârtha between 558–569. (2) 觀所緣緣論, T 1624, translated by Xuanzang in 657; (3) 觀所緣論釋 (Dharmapālaʼs commentary) T 1625, translated by Yijing in 710. There are several translations and studies of this text, including:

   Lü Cheng 呂澂, 觀所緣釋論會譯 Guan suoyuan shi lun huiyi. [A Comparative Exposition of the texts of the Ālambana-parīkṣā. ] (Ch. translation of the Tibetan version, with annotated versions of the Paramârtha, Xuanzang, and Yijing / Dharmapāla texts), Neixue Disiji. , 1928, 761-806;

   Hidenori Kitagawa, インド古典論理学の研究; 陳那 (Dignāga) の体系 [Indo koten ronrigaku no kenkyū; Jinna (Dignāga) no taikei. (A Study of a Short Philosophical Treatise Ascribed to Dignāga)] [partial translation of the Qu yin jiashe lun. ], Tokyo, 1965;

   Hakuju Ui, Jinna chosaku no kenkyū. , Tōkyō, 1958;

   Yamaguchi Susumu, Seshin yuishiki no genten kaimei. , Kyoto, 1953;

   Yamaguchi Susumu with Harriette Meyer, Examen de l'objet connaissance. , Paris: Imprimerie Nationale, 1929;

   Magdalene Schott, Sein als bewusstsein; ein beitrag zur Mahāyāna-philosophie. , [German translation of the Dharmapāla commentary] Heidelberg, 1935;

   F. Tola and C. Dragonetti, Dignāga's. Ālambanaparīkṣavṛtti, Journal of Indian Philosophy 10 (1982) 105-134.

4. Hastavālaprakaraṇa. (1) 解捲論, T 1620, translated by Paramârtha between 558–569; (2) 掌中論, T 1621, translated by Yijing in 702. The Tibetan tradition attributes this short text to Āryadeva, not Dignāga, but both Chinese versions assign it to Dignāga. It discusses the rope-snake analogy, correct cognition, etc. An English translation (from the Tibetan), accompanied by a reconstructed Sanskrit version, the Tibetan and two Chinese versions was published by F.W. Thomas and H. Ui, “ 'The Hand Treatise,' A Work of Āryadeva,” Royal Asiatic Society of Great Britain and Ireland, April 1918, 267–310.
5. Upâdāya-prajñapti-prakaraṇa 取因假設論, T 1622, translated by Yijing in 703.
6. Sāmānya-lakṣaṇa-parīkṣā 觀總相論頌, T 1623, translated by Yijing in 711.
7. Prajñāpāramitā-saṃgraha-kārikā 佛母般若波羅蜜多圓集要義論, T 1518, translated by Dānapāla in 1011. Verses summarizing Prajñāpāramitā thought.
8. Prajñāpāramitā-saṃgraha-kārikā-vivaraṇa 佛母般若波羅蜜多圓集要義釋論, T 1517, translated by Dānapāla. A commentary to the kārikās.

Among Dignāgaʼs other works that were not translated into Chinese are his Hetacakraḍamaru which presents his 9-point model for differentiating valid from invalid 'reasons' (cf. D.C. Chatterjee, “Hetucakranirṇaya,”  Indian Historical Quarterly, 10 (1933) 266–72, 511–14; Eli Franco, “A Note of Hetucakraḍamaru 8–9,”  Indo-Iranian Journal, 36 (1993); Lambert Schmithausen, “A Further Note on Hetucakraḍamaru 8–9,” Journal of Indian Philosophy, 27 (1999) 79–82; and Richard S.Y. Chi, Buddhist Formal Logic, Delhi: Motilal Banarsidass, 1984) and a commentary on the Abhidharmakośa. For a thorough listing of Dignāgaʼs known works, see the Introduction to M. Hattori, Dignāga, On Perception, pp. 6–10.

Xuanzangʼs translation of Śaṃkarasvāminʼs Nyāyapraveśa 因明入正理論, T 1630, should also be mentioned, since it is an introductory summary to Dignāgaʼs system of inference. The Sanskrit version is extant, and an edition of the Skt with English translation is Musashi TACHIKAWA, “A Sixth-century Manual of Indian Logic,” Journal of Indian Philosophy 1 (1971) 111–145.