In the course of the development of the Yogacara school there exist different stages in the manner in which the doctrine of the three selfnatures (trisvabhdva=parikalpita-svabadva, paratantra-svabadva and parinispanna-svabhava) is explained. The stages are classified into four ; (1) the first, corresponding to the Samdhinirmocana-sutra and the Yogagacarabhumi, (2) the second, including the Mahayanasutralamkara and the Madhyantavibhaga, (3) the third of the Mahayanasamgraha, and (4) the fourth of the Trimsikakarika. In the first stage, each of the three self-natures is not yet explained in relation to epistemology. In the second stage, the "dependent self-nature" (paratantra-svabhava) is identified with "unreal ideation" (abhuta parikalpa) as the subject of cognition and the "ideated self-nature" (parikalpita-svabhava) as the object (artha). In the third stage, the doctrine of the three self-natures and that of "Consciousness-only" (vijnapti-matra) are unified and consequently the object of cognition comes to be immanent in the "consciousness" (vijndna) of the "dependent self-nature". In the fourth stage, the understandings in the second and the third stage are unified with each other. There are several differences between Sthiramati's understanding of the three self-natures doctrine and that of Dharmapala ; I assert that the point at which those differences start lies between Maitreya and Asanga. In Maitreya's understanding of the three self-natures doctrine, the "dependent self-nature" was the subject and the "ideated self-nature" the object of cognition ; whereas for Asanga, both the subject and the object of cognition are immanent in the "consciousness" (vijndna). These two different understandings come to be unified in Vasubandhu. With regards to the three self-natures doctrine occuring in the 17th verse of the Trimsikakarika of Vasubandhu, I argue that Sthiramati's understanding is inherited from Maitreya's and Dharmapala's from Asanga's.
