成唯識論述記 3.305

3.305

述曰：謂作意生心，是籌度心，即六、七識，隨自分別作意生故。由此六、七緣無等時，影像相分，無有實體，未必有用。亦非由說分別，故變境體定無，亦緣有故。或初通五、八全，及第六少分；後第七全，通第六少分。此解順論有用等文。

The Commentary states: This refers to the mind produced through mental application, which is a mind of deliberation, namely, the sixth and seventh consciousnesses, because they arise in accordance with their own conceptual discrimination and mental application. Because of this, when the sixth and seventh take non-existence and the like as objects, the nimittabhāga of the image has no real substance and does not necessarily have utility. Nor is it that because they are called conceptual discrimination, the substance of the transformed object is definitely non-existent, for they also take existent things as objects. Or: the first includes the whole of the five and the eighth, and a small part of the sixth; the latter includes the whole of the seventh and extends to a small part of the sixth. This interpretation accords with the treatise's text on 'having utility,' etc.