成唯識論述記 5.476

5.476

述曰：《莊嚴論》、《攝論》第九，轉第七得平等智，平等智定有所依識，故有第七淨也。量云：平等性智定有別所依識；說轉得故；如餘三智。第七若無，即平等智亦應非有，非離所依心有能依智故。

The Commentary states: The Mahāyānasūtrālaṃkāra and chapter 9 of the Mahāyānasaṃgraha state that by transforming the seventh consciousness one obtains the wisdom of equality (samatājñāna). The wisdom of equality must have a consciousness on which it depends; therefore, there is a pure seventh consciousness. The formal syllogism is: The samatā-jñāna definitely has a distinct consciousness upon which it depends; because it is said to be obtained by transformation; like the other three wisdoms. If the seventh did not exist, then the wisdom of equality should also not exist, for there cannot be a dependent wisdom apart from a mental locus of dependence.