摩訶止觀 3.124

3.124

但空、不但空合時秖是一真諦；離時成兩真諦，與三藏家異。彼三藏第三諦，但有中道名，無別體。眼無別見，智無別知。今則不爾。第三諦亦名「真諦」，亦名「中道第一義諦」，有別體、別見、別知。是為通教二諦、三諦離合之相也。

When combined, mere emptiness and not-mere-emptiness are just one ultimate truth; when separated, they become two ultimate truths, differing from the Tripiṭaka school. In the Tripiṭaka school, the third truth has only the name of the middle way, but has no distinct substance. The eye has no distinct seeing, and wisdom has no distinct knowing. Now it is not so. The third truth is also called 'ultimate truth', and also called 'the ultimate truth of the middle way'; it has a distinct substance, distinct seeing, and distinct knowing. This is the mark of separation and combination of the two truths and three truths in the shared teaching.