Vasubandhu’s emergence as a co‑founder of Yogācāra can be understood as the fruit of a profound inner and intellectual transformation. He first distinguished himself as a master of Sarvāstivāda Abhidharma, composing the *Abhidharmakośa* and its commentary as a rigorous exposition of that school’s analysis of dharmas. At this stage his orientation was aligned with a more “realist” Abhidharma framework, and he was not yet a proponent of consciousness‑only thought. This early formation gave him both the analytical tools and the reputation that later allowed his shift toward Yogācāra to carry great weight within the Buddhist world.

The turning point came through the influence of Asaṅga, already a major Yogācāra figure and closely connected to Vasubandhu in traditional accounts. Asaṅga gradually exposed him to Mahāyāna and Yogācāra teachings, using skillful means to draw him beyond the limits he perceived in his earlier Abhidharma position. Through study of Yogācāra materials associated with Asaṅga, Vasubandhu became convinced of the depth of the consciousness‑only (vijñaptimātra or citta‑mātra) perspective and the doctrine of the storehouse consciousness (ālaya‑vijñāna). This conversion was not merely a change of opinion but a reorientation of his understanding of reality and the path, which he acknowledged by setting aside his former stance.

Once this transformation had taken root, Vasubandhu turned his formidable analytical skills toward clarifying and systematizing Yogācāra. He distilled the sprawling earlier tradition into concise, philosophically precise treatises such as the *Viṃśatikā* and *Triṃśikā*, along with commentarial work that articulated key doctrines. Within these writings, he set out the core Yogācāra themes: consciousness‑only, the storehouse consciousness, the theory of seeds and karmic imprints, and the three natures (trisvabhāva), as well as a detailed account of the eight types of consciousness. His use of careful logical argumentation made these ideas accessible and compelling to other scholars.

Through this combination of conversion, systematization, and rigorous defense of Yogācāra thought, Vasubandhu came to stand alongside Asaṅga as one of the tradition’s principal architects. Asaṅga is remembered as the pioneering figure who first gave Yogācāra its broad visionary and textual foundation, while Vasubandhu is honored as the one who refined, stabilized, and completed its philosophical core. In this way, his journey from Abhidharma master to Yogācāra thinker exemplifies how deep questioning and disciplined reflection can reshape an entire spiritual lineage, giving it a clear doctrinal identity that would resonate across later Buddhist cultures.