大乘百法明門論開宗義決 1.142

1.142

如非四境率爾墮心者。如非所樂決定曾習所觀四境。無四境處都無別境。率爾墮心者。謂諸心起有五種心。一者率爾。二者尋求。三者決定。四者染淨。五者等流。識初墮境名率爾墮。雖緣善惡未知善惡。次起尋求既識善惡。次起決定。既決定已便起染淨。於怨住惡。於親住善。於中住捨。一剎那後同性而起名等流心。於五心中。染淨心後方有欲等。故初墮在率爾心時無別境也。

Regarding "just as [when experiencing] what is not of the four objects, the mind falls [upon it] abruptly": this means that, just as when one does not experience the four objects that are either desired, determined, previously practiced, or contemplated, where in the absence of the four objects there is no distinct object at all; "the mind falls [upon it] abruptly" means that among the arisings of mind, there are five kinds of mind: first, the abrupt mind; second, the inquiring mind; third, the determining mind; fourth, the defiled or pure mind; fifth, the flowing mind. When consciousness first falls upon an object, it is called falling abruptly; although it takes good or bad as its object, it does not yet distinguish between good and bad. Next arises inquiry, which recognizes good and bad. Next arises determination. Once determined, the defiled or pure [mind] then arises: towards enemies it dwells in bad, towards friends it dwells in good, and towards the neutral it dwells in equanimity. After one moment, that which arises sharing the same nature is called the flowing mind. Among the five minds, only after the defiled or pure mind are there desire and the like; therefore, when it first falls into the abrupt mind, there is no distinct object.