八識規矩補註 1.12

1.12

Saying here that the five consciousnesses obtain the name of 'subtle form' refers to the ultimate sense: their substance is not a defiled dharma, but of exclusively pure, anivṛtāvyākṛta nature. The five consciousnesses are named according to their bases, possessing five meanings in all: relying, generating, belonging, and assisting, as stated in the verse. 'Relying' is one of the five meanings. If analyzed as a compound: the consciousness that relies on the base, or assists the base, or is like the base, are all tatpuruṣa compounds; the consciousness generated by the base is also a tatpuruṣa compound, or saying 'the consciousness generated by the base' provides yet another example.