成唯識論述記 8.189

8.189

述曰：此謂第八於餘七識有所緣緣義，七於第八無此緣義。以第八相色等為其本質，生五識相分色等故；第七亦緣彼見分為境故；第六理通以相、見為境，若無第八定為本質，五、七不生故。雖非親所緣緣，然是疎所緣緣也。第八不託七識而生故，七非八所緣緣也。第八若有，七識必有，七但為八定有增上緣，非所緣緣也。

The Commentary states: This means that the eighth consciousness has the sense of being an objective condition (ālambana-pratyaya) for the remaining seven consciousnesses, while the seven do not have this sense of being such a condition for the eighth. This is because the form (rūpa) and so forth of the eighth consciousness's nimittabhāga serve as the underlying archetype (vastu/ālambana) that gives rise to the form and so forth of the five consciousnesses' nimittabhāga; the seventh consciousness also grasps the eighth's darśanabhāga as its cognitive object; and the sixth consciousness, by principle, universally takes both the nimittabhāga and darśanabhāga [of the eighth] as its cognitive object, for without the eighth definitely serving as the underlying archetype, the five and the seventh would not arise. Although it is not an immediate objective condition (pratyakṣa-ālambana-pratyaya), it is a mediate objective condition (dūra-ālambana-pratyaya). Because the eighth consciousness does not arise by relying on the seven consciousnesses, the seven are not objective conditions for the eighth. If the eighth consciousness exists, the seven consciousnesses necessarily exist; the seven merely serve as definite predominant conditions (adhipati-pratyaya) for the eighth, not objective conditions.