成唯識論述記 3.200

3.200

述曰：明四分中，自下第三說有四分。於中有四，初立四理；二分別之；三引教成；四釋頌意，下即初也。護法以後，方始立之，理極須然，如文可解，然諸經論唯多三分。

The Commentary states: Under the explanation of the four parts, the third section below states that there are four parts. In this, there are four points: first, establishing the four reasons; second, analyzing them; third, citing teachings to confirm them; fourth, explaining the meaning of the verses. The following is the first point. Only from Dharmapāla onward was this first established; in reason it is absolutely necessary, and can be understood from the text; yet various sūtras and treatises mostly mention only three parts.