二諦義 1.24

1.24

問曰：二諦與四悉檀攝法皆盡，何意諸佛依二諦說法，不依四悉檀說耶？解云：通皆得。既依二諦說，亦依四悉檀說。別即不例。何者？此有義，欲明諸佛所說皆實。《金剛波若》云「如來是真語者、實語者」，是故依二諦說。四悉檀名不的主實，是故不依四悉檀說也。

Question: Since the two truths and the four siddhāntas both subsume all phenomena exhaustively, for what reason do all Buddhas expound the Dharma based on the two truths and not based on the four siddhāntas? It is explained: Generically, both are permissible: since they expound based on the two truths, they also expound based on the four siddhāntas. Specifically, they are not parallel. Why? There is a reason for this: [the Buddha] wishes to make clear that all that the Buddhas speak is real. The Vajracchedikā Prajñāpāramitā states: "The Tathāgata is one who speaks the true, one who speaks the real." Therefore, they expound based on the two truths. The designation "four siddhāntas" does not specifically emphasize the real, and therefore they do not expound based on the four siddhāntas.