[W]hen various groups of retinues are examined in terms of the Four Teachings, they are classified by Chih-i into coarse or subtle. Retinues that belong to the Tripiṭaka, the Common and the Separate Teachings are coarse, except for the ones of the Perfect Teaching that are subtle. As the Perfect Teaching concerning universal salvation that is represented by the Lotus Sūtra, Chih-i maintains that in the Lotus Sūtra, all retinues of the Buddha are considered to be subtle. For Chih-i, the Four Teachings are the four ways of reaching truth, and thus, are the four Dharma-doors. (vOL. 2, Page 293)