Which consciousness neither thinks of good nor thinks of evil?

Question: The five universal mental factors should be present in all eight consciousnesses, so why is it that [the eighth consciousness] still does not think of good or think of evil?

Answer: Although all eight consciousnesses possess the five universal mental factors—manaskāra (attention), sparśa (contact), vedanā (feeling), saṃjñā (perception), and cetanā (volition)—each consciousness does not apply attention, contact, feeling, perception, and volition to all dharmas; it is selective. The object-aspects of each consciousness differ greatly, and each consciousness only applies attention, contact, feeling, perception, and volition to the object-aspect corresponding to itself; it will not apply them to object-aspects that do not correspond to it. Moreover, the six consciousnesses arise and cease incessantly; once they cease, they no longer have the five universal mental factors with respect to any dharma.

"Not thinking of good and not thinking of evil" means that the eighth consciousness has never deliberated on the dharma-marks of good and evil, whereas the sixth consciousness and the seventh consciousness always deliberate on the dharma-marks of good and evil. If one cultivates to a certain degree, the sixth and seventh consciousnesses will also cease to deliberate on the dharma-marks of good and evil, and will instead see the tathatā essence of the dharma-marks of good and evil.