成唯識論述記 3.202

3.202

述曰：此立理也。第三、第二心分既同，應立別有能證自分。量云：第三分心應有能照之心；心分攝故；猶如見分。見分返此，或無能證。

The Commentary states: This establishes the reasoning. Since the third and second parts of the mind are alike, one should establish a distinct part capable of confirming oneself. The syllogism is: The third part of the mind should have a mind capable of illuminating it; because it is subsumed under mental parts; just like the darśanabhāga. The darśanabhāga is the contrary of this, or it would have nothing to confirm it.