Some six hundred verses set out the system of the Vaibhāṣikas, the scholastics who dominated Buddhist learning in Kashmir, and a prose commentary by the same hand keeps asking whether they are right. That book, the Abhidharmakośa-Bhāṣya, is Vasubandhu's best known, and its closing verses concede that the system they explain is mostly the Kashmiri masters'. Again and again his commentary sides with the Sautrāntikas, Buddhists who trusted the Buddha's discourses over the scholastic treatises. A master reporting a doctrine and testing it in the same pages: that double voice runs through all his work.
The doctrine at stake was the Buddha's teaching that there is no lasting self. Abhidharma, the Buddhist analysis of experience, had made that teaching precise by breaking a person down into dharmas, momentary factors of body and mind. It left a hard question. If every factor vanishes as soon as it arises, how does a deed done years ago bear its fruit, and what carries a memory forward? The Vaibhāṣikas answered that past and future factors exist as truly as present ones. Vasubandhu's commentary rejects this: only the present exists; a thing perishes of itself, since destruction needs no cause, and a past action survives as a seed in the stream of mind until it ripens.
Two sources tell how he came to these questions: the biography that Paramārtha, an Indian translator, wrote in sixth-century China, and the later account of the Chinese pilgrim Xuanzang. He was born in Puruṣapura, today's Peshawar, the younger brother of Asaṅga, a monk of the Mahayana, and he trained in the Sarvāstivāda school whose Kashmiri masters were the Vaibhāṣikas. Paramārtha tells that those masters welcomed the verses of the Kośa and turned against it when the commentary followed. Saṅghabhadra, a Vaibhāṣika master of the same generation, wrote two treatises to refute it and came to Ayodhyā, where Vasubandhu lived under royal patronage, to challenge him to a debate; Vasubandhu declined, saying he was old.
The turn came, the tradition says, through his brother. Asaṅga feared that Vasubandhu's gifts would be used against the Mahayana, feigned illness to bring him to Puruṣapura, and won him over. Ashamed of having disparaged the Mahayana, Vasubandhu wanted to cut out his tongue; Asaṅga told him to use it for the Mahayana instead. Scholars read the turn in other ways. In 1951 Erich Frauwallner, the Austrian Indologist, proposed that the biographies had merged two men named Vasubandhu, a hypothesis that still divides the field; others see a gradual development rather than a conversion. Historians place him in the fourth or fifth century CE. No year is secure.
The claim he is remembered for is vijñaptimātra, "representation only": everything we meet in experience is the mind's own representation, and objects standing outside the mind are not found. The Viṃśatikā-kārikā-vṛtti, the Twenty Verses, defends it against a realist with ordinary cases. In dreams, too, things appear in fixed places and at fixed times. Hungry ghosts, beings reborn in torment by their own greed, all see the same river of pus because their past deeds are alike. And an atom joined on six sides to six others must have six parts, so it is no atom, and nothing can be built of atoms. The thesis is not that nothing exists. The verses he explained in Distinguishing the Middle from the Extremes, which the tradition ascribes to Maitreya, the coming Buddha, make the point: the mind's imagining is real; what is unreal is its split into a grasping subject and a grasped object. The Triṃśikā-kārikā places freedom where consciousness stops grasping any object at all.
The tradition credits him with a thousand works, five hundred for each of the two vehicles of Buddhism; some forty-seven survive. Dignāga, who founded Buddhist logic, is counted among his pupils in Tibetan accounts. Sthiramati, a sixth-century scholar of his school, commented on several of his books, and Xuanzang fused ten Indian commentaries on the Thirty Verses into one treatise, the founding text of the Faxiang school in China and of Hossō in Japan. Traditions from India to China call him a bodhisattva, or even a second Buddha. Much of his Sanskrit was lost for centuries: Sylvain Lévi, the French Indologist, found the Twenty and Thirty Verses in Nepal in 1922, and Rāhula Sāṅkṛtyāyana, an Indian scholar travelling in Tibet, found the Kośa at Ngor monastery in the 1930s.