Step 1: Asaṅga’s contribution.
Ācārya Asaṅga, a prominent Buddhist scholar of the 4th century, founded the Yogācāra school, also known as Vijñānavāda.
Step 2: Yogācāra philosophy.
This school is based on the principle of consciousness-only (Vijñapti-mātratā). Asaṅga elaborated on this philosophy in his works, such as the Yogācārabhūmi-śāstra.
Step 3: Options analysis.
- (1) Sautrāntika: A Sūtra-centric school, not associated with Asaṅga.
- (2) Vaibhāṣika: An Abhidharma-centric school, not founded by Asaṅga.
- (3) Mādhymika: The tradition of Nāgārjuna and Āryadeva.
- (4) Yogācāra: Correct, Asaṅga founded the Yogācāra school.
Step 4: Conclusion.
The correct answer to this question is Yogācāra.