成唯識論述記 8.88

8.88

述曰：雖八因內，四因中有非方便因，謂因緣種等，以四因全四、少分中，增上多故，論乃偏說是方便因，即前能生因，隱增上者，後方便因，隱因緣者，俱不明故，為不盡理也。

The Commentary states: Although within the eight causes, four causes contain what are not auxiliary causes—namely, seeds that are cause-conditions and the like—nevertheless, because in all four causes and in parts of the [other] four, the dominant [aspect] is predominant, the treatise specifically says they are auxiliary causes. That is, the former productive cause conceals the dominant, and the latter auxiliary cause conceals the cause-conditions; neither is completely clear, and so [the phrasing] does not fully express the underlying principle.