俱舍論疏 24.107

24.107

論「道類智至必總緣故」，釋道必總緣也。緣八地道總有四行，相應有四，以治八地，類智品道同類相因必總緣故。緣滅唯別，緣道即不爾，以類同故、互相因故。

The Śāstra says: "The subsequent knowledge of the path […] because it must take them collectively." This explains why the path must be taken collectively. Taking the paths of the eight stages as its object, there are four aspects in total, with four associated [aspects], because the paths of the subsequent knowledge category that remedy the eight stages are homogeneous causes of one another and must be taken collectively. Taking cessation as object is exclusively separate, but taking the path as object is not so, because they are of the same category and serve as mutual causes.