大乘起信論義記 2.156

2.156

Furthermore, turning to another objection: Since it is said that the marks of consciousness are all avidyā, and therefore they are said to be extinguished, they should have a separate substance apart from tathatā. This is the objection of real and false having separate substances. The answer says: The marks of non-enlightenment of these various consciousnesses are not separate from the nature of innate enlightenment that follows defilement; for this reason it says they are 'not separate from the nature of enlightenment.' These marks of avidyā and that nature of innate enlightenment are neither one nor different. Because they are not different, they are not destructible; because they are not one, they are not indestructible. If one relies on the meaning of non-difference and being indestructible, it is said that avidyā is identical with clarity; hence the Nirvāṇasūtra says: 'Clarity and avidyā are not dual in their nature; the nature of non-duality is itself the true nature.' If one approaches it through the meaning of not being one and not being indestructible, it is said that avidyā is extinguished while the nature of enlightenment is not destroyed. The meaning of extinguishing delusion should be understood accordingly.