Cheng Weishi Lun (, CWSL, Sanskrit reconstruction: *Vijñapti-mātratā-siddhi, English: The Demonstration of Consciousness-only, Taisho Catalog number 1585), is a comprehensive treatise on the philosophy of Yogacara Buddhism and a commentary on Vasubandhu's seminal work, the Triṃśikā-vijñaptimātratā (Thirty Verses on Consciousness-only).
The CWSL was written by the early Tang dynasty monk Xuanzang (602–664), who drew on the commentarial work of 10 different Indian Yogacara scholars as well as his experience of studying under the Indian Yogacara master Śīlabhadra in Nalanda University.
When Xuanzang was studying Buddhism in India at Nālandā University, he studied ten commentaries on Vasubandhu's Triṃśikā-vijñaptimātratā. Back in China, Xuanzang drew upon these commentaries, especially the commentary of master Dharmapāla, to write a detailed explanation of Vasubandhu's Triṃśikā-vijñaptimātratā. This synthetic commentary became the Cheng Weishi Lun.
According to Francis Cook, The theory of the Ch’eng wei-shih lun is that basic or fundamental consciousness (mula-vijñana) comes to appear naturally and spontaneously in the form of a seeing part (darsana-bhaga) and a seen part (nimitta-bhaga). The seeming reality of an inner self perceiving external events is nothing more than one aspect of consciousness perceiving itself in the form of images. A third part of consciousness, the manas, or thinking aspect, interprets the two parts as a self and an external world. This situation is also the basis for hatred, craving, fear, and other passions. In fact, the apparently real external world of things is nothing but internal images perceived by consciousness and grasped as a source of attachment by thought.The Chéng Wéishì Lùn became one of the key texts of East Asian Yogācāra, both by Chinese ("Faxiang") and Japanese ("Hossō") thinkers. It is a major doctrinal source and summa for this tradition, also known as the Consciousness Only School (Wéishí-zōng).
Kuiji, one of Xuanzang's key pupils, wrote a commentary on the CWSL, called the Chéng Wéishì Lùn Shuji (成唯識 論述記; Taishō no.