Asaṅga was born as the son of a Kṣatriya father and Brahmin mother in Puruṣapura (present day Peshawar in Pakistan), which at that time was part of the ancient kingdom of Gandhāra. Current scholarship places him in the fourth century CE. In the record of his journeys through the kingdoms of India, Xuanzang wrote that Asaṅga was initially a Mahīśāsaka monk, but soon turned toward the Mahāyāna teachings. According to legend, Asanga's meditation practice allowed him to enter the heavens, wherein he studied the teachings that he brought to the world of form.
In the great mango grove five or six li to the southwest of the city (Ayodhyā), there is an old monastery where Asaṅga Bodhisattva received instructions and guided the common people. At night he went up to the place of Maitreya Bodhisattva in Tuṣita Heaven to learn the Yogācārabhūmi-śāstra, the Mahāyāna-sūtra-alaṃkāra-śāstra, the Madhyānta-vibhāga-śāstra, etc.; in the daytime, he lectured on the marvelous principles to a great audience. (Xuanzang)
Asaṅga's half-brother, Vasubandhu, was a monk from the Sarvāstivāda school. They were both students of Abbidharma, a subject which was the precursor to many key concepts and Yogacare, and on which Vasubandhu wrote in great detail. According to The Great Tang Dynasty Record of the Western Regions, Vasubandhu took up Mahāyāna Buddhism after meeting with Asaṅga and one of Asaṅga's disciples.
Asanga introduced the idea of four ways of knowing: the perfection of action, observing knowing, universal knowing, and great mirror knowing. He relates these to the Eight Consciousnesses:
In time, these ways of knowing were also connected to the doctrine of the three bodies of the Buddha (Dharmakāya, Sambhogakāya and Nirmanakaya), together forming the "Yuishiki doctrine". Hakuin related these four ways of knowing to four gates on the Buddhist path: the Gate of Inspiration, the Gate of Practice, the Gate of Awakening, and the Gate of Nirvana: