請觀音經疏闡義鈔 2.49

2.49

「但眼」下，結示三性。若論本性，自具三因。眼根即中是正、即空是了、即假是緣，今作一性二修示之。「但眼之本」等者，即指本具中理為正因，此即合性為一也。「了此」等者，謂修觀了達也。

From "merely the eye" downward concludes by demonstrating the three natures. If one speaks of the fundamental nature, it inherently possesses the three causes. The eye faculty is the direct [cause] as the middle, the revealing [cause] as empty, and the contributory [cause] as the provisional; now it is shown by making one nature and two cultivations. "Merely the root of the eye," and so forth, points directly to the inherently possessed principle of the middle as the direct cause; this combines the nature into one. "Comprehending this," and so forth, refers to fully comprehending through cultivating contemplation.