成唯識論述記 1.426

1.426

返為量云：汝之三事未成大等時，應亦能成大等；前與後體無差別故；如後成時。第八，彼言三體有異，其相是一，即救前難，故為此計。

In reverse, the syllogism is: When your three entities have not yet established mahat and so forth, they should also be able to establish mahat and so forth; because between before and after the essence is without distinction; like when they are subsequently established. Eighth, they say that the three essences are different while their characteristic is one; this rescues them from the previous objection, and so they advance this position.