大乘百法明門論開宗義決 1.108

1.108

勿真如性亦名能緣等者。此中意云。若正體智許無見分而能緣者。則應真如亦合能緣。無見分故。勿猶莫也。以正智無見分故而成能緣。令真如性成能緣義。既真如性無見分故不成能緣。故正體智是能緣故必有見分。

Regarding "Lest the nature of tathatā also be called a cognizer": the meaning here is that if it were conceded that the fundamental wisdom (mūla-jñāna) lacks a subjective aspect yet is able to cognize, then tathatā should likewise be able to cognize, because it lacks a subjective aspect. "Lest" (勿) means "do not let" (莫). If because fundamental wisdom lacks a subjective aspect it becomes a cognizer, this would cause the nature of tathatā to have the meaning of being a cognizer. Since the nature of tathatā lacks a subjective aspect and therefore does not become a cognizer, fundamental wisdom, being a cognizer, must have a subjective aspect.