大乘起信論廣釋卷第三．四．五 3.72

3.72

[Treatise:] It is named mental consciousness [...] discriminating phenomenal consciousness. [Commentary:] This establishes its name. Since it conditions the six sense-objects, it should be named the six consciousnesses; but here, with respect to its sense as a single mental consciousness, the five consciousnesses of the eye and so on are not separately brought out. Thus the Nirvāṇa [Sūtra] says: "Like a single consciousness, it is discriminately called six." The Suvarṇaprabhāsa Sūtra says: "The mind is like an illusion, galloping through the six sense-objects, constantly falsely generating discrimination of all dharmas." Therefore, conditioning the six sense-objects is merely named mental consciousness. This very mental consciousness relies on the six sense-faculties to separately grasp the six sense-objects, hence it is called "separative." Furthermore, because it can discriminatively know coming and going, internal and external, good and evil, causes and effects, and various phenomenal characteristics, it is also called "discriminating phenomenal consciousness."