妙法蓮華經玄義 5.144

5.144

五品弟子，假名四悉檀。六根淨，相似四悉檀。初住至等覺，分真四悉檀。妙覺，究竟四悉檀，是故稱妙。

For disciples of the five grades, it is the nominal four siddhāntas. For the purification of the six sense faculties, it is the resemblance four siddhāntas. From the first abidance to virtual awakening, it is the partial-real four siddhāntas. At wondrous awakening, it is the ultimate four siddhāntas; therefore it is called subtle.