成唯識論述記 8.191

8.191

述曰：第七於餘前之六識，於初五識，無此緣義。與一意識為所緣緣，意緣一切法故，五識無者不緣七故，前之六識於第七識，並非彼所緣緣，彼不緣六故，自是一行法故不問八。

The Commentary states: The seventh consciousness, in relation to the remaining previous six consciousnesses, lacks the sense of being this condition with respect to the first five consciousnesses. It serves as an objective condition only for the single mental consciousness (manovijñāna), because the mental consciousness cognizes all dharmas; that it does not serve for the five consciousnesses is because they do not cognize the seventh. The previous six consciousnesses, in relation to the seventh consciousness, are not its objective conditions at all, because it does not cognize the six; since it is exclusively a single mode of practice, it does not inquire about the eighth [here].