大乘起信論裂網疏 3.44

3.44

Although arising and ceasing has no intrinsic nature and is entirely tathatā, yet tathatā is immutable yet accords with conditions; when its entire essence becomes arising and ceasing, within arising and ceasing one must discuss causes and conditions, only then avoiding the faults of heterodox causes and causelessness. In this way, the eighth and the prior seven consciousnesses become mutual causes and effects, and the principle of vijñaptimātra is established. 'Sentient beings' is a provisional designation for the harmony of the five aggregates. 'Mind' is the eighth consciousness. 'Thought' (manas) is the seventh consciousness. 'Mental consciousness' (manovijñāna) is the sixth consciousness together with the first five consciousnesses. With the eighth as the fundamental basis, the seventh then operates. With the seventh as the defiled and pure basis, the sixth then operates. With the sixth as the basis of discrimination, the first five then operate. Therefore it is said that they operate based on mind, thought, and mental consciousness.