大般涅槃經集解 66.96

66.96

案僧亮曰：常是果性、無常是因性，二俱性不偏，名為中也。僧宗曰：凡夫所計，理則不然。佛性之理，理非內外，先舉六入以顯義也。若言但內，二俱不當也。今言佛性假內假外合用者，即有正因、即有境界因，不離此而成，故就合用之功以為中道也。就辨合用中有五翻，此即第一翻也。

Sengliang notes: Permanence is the nature of the fruit; impermanence is the nature of the cause. Both being natures without bias is called 'the middle'. Sengzong says: What ordinary people reckon is not so in principle. The principle of buddhadhātu is neither internal nor external; it first cites the six sense-bases to reveal the meaning. If one said it were only internal, neither [view] would be appropriate. Now, stating that buddhadhātu relies provisionally on the internal and the external in combined functioning means that there is both a primary cause and an objective condition-cause; it is accomplished without departing from these. Hence, with reference to the efficacy of their combined functioning, it is considered the middle way. Within the analysis of combined functioning there are five rounds, and this is the first round.