仁王護國般若波羅蜜多經疏 2.21

2.21

Question: Mindfulness (smṛti) has clear recollection as its nature among the particular mental factors; why is it said here that a thought-moment (smṛti/kṣaṇa) arises, ceases, and is empty? Answer: The word *nian* is the same, but that to which it refers differs. That mindfulness among the particular mental factors has clear recollection as its nature; this one is nominally designated within time among the non-associated formations: the span of a single arising and ceasing is provisionally designated with the name "thought-moment." The thought-moment has no real substance and is entirely empty. Next is the fourth [part], concluding on the emptiness of all phenomena.