摩訶止觀 9.143

9.143

如其不悟，即塞而不通，應當更觀何者不通，何者不塞。若其不塞，即應是通；如其不通，更須觀察。知字非字，識四諦得失。

If one still does not awaken, then there is obstruction without passage. One should further contemplate what does not pass through and what is not obstructed. If it is not obstructed, it should be passage; if there is no passage, one must observe further, knowing what is letter and what is non-letter, and discerning the gains and losses of the four truths.