成唯識論述記 4.886

4.886

述曰：不然，即有不明了失，與五相望可為例故。如《瑜伽》論五十五說：有分別心、無分別心同緣現在境，由三因故，一極明了等。若彼意識不依五識，亦應不與五識為依，五、六相望勢力等故。五識賴意引而方生，意識由五同而明了故。

The Commentary states: If not, then there would be the fault of not being lucid, because looking toward the five it can serve as a parallel. As Fascicle 55 of the Yogācārabhūmi states: conceptual mind and non-conceptual mind cognize present objects together due to three causes, the first being extreme lucidity, and so forth. If that mental consciousness did not depend on the five consciousnesses, it also should not serve as a support for the five consciousnesses, because the power between the five and the sixth is equal. The five consciousnesses rely on the mind to be led before they arise, and mental consciousness is lucid by sharing with the five.