俱舍論記 11.58

11.58

「何故月輪至見有缺耶」者，問。黑半漸盡故言末，非是末後也。除第十五日已前十四日，皆名白半初。又解：於黑白十五日中，近後名末、近前名初。雖黑半中從十六日已去漸缺，白半中至十四日已來亦有缺，以未及初缺相顯故。

Regarding "Why is the lunar disk seen to have a wane?": This is a question. Because the dark fortnight gradually ends, it is called the end, not the very last. Excluding the fifteenth day, the preceding fourteen days are all called the beginning of the bright fortnight. Another explanation: Among the fifteen days of the dark and bright [fortnights], those closer to the end are called the end, and those closer to the front are called the beginning. Although in the dark fortnight it gradually wanes from the sixteenth day onward, in the bright fortnight up to the fourteenth day it also has a wane, because it has not yet reached the beginning, and the phase of wane is visible.