大般涅槃經義記 7.53

7.53

「云何生不生不可說」者牒問第三。「生即名生」以前破後。良以生者即名生故非定不生。「生不自生」以後破前。向前生相但能生他故名為生，自體非生。體非生故名為不生。以不生故，不可定說以之為生。「不可說」者生與不生皆悉不定故不可說。

"How is it that the arising of non-arising cannot be spoken of?" cites the question regarding the third. "Arising is indeed termed arising" uses the prior to refute the subsequent. It is precisely because what arises is immediately termed arising that it is not definitively non-arising. "Arising does not arise of itself" uses the subsequent to refute the prior. The aforementioned mark of arising can only produce others, and is thus called arising; its own essence does not arise. Since its essence does not arise, it is called non-arising. Because it does not arise, it cannot be definitively spoken of as arising. "Cannot be spoken of" means that because both arising and non-arising are non-definitive, they cannot be spoken of.