成唯識論述記 3.196

3.196

述曰：相分、見分、自體三種，即所、能量、量果別也，如次配之。如以尺丈量於物時，物為所量，尺為能量，解數之智名為量果，心等量境，類亦應然，故立三種。若無自證分，相、見二分無所依事故，即成別體，心外有境。今言有所依故，離心無境，即一體也。

The Commentary states: The three—nimittabhāga, darśanabhāga, and intrinsic substance—are the distinctions of the object of measure (prameya), the means of measure (pramāṇa), and the result of measure (pramāṇaphala), matched respectively. Just as when measuring an object with a measuring rod, the object is the prameya, the rod is the pramāṇa, and the cognition understanding the number is called the pramāṇaphala; when the mind and the like measure an object, it should by analogy also be like this, hence three kinds are established. If there were no svasaṃvittibhāga, the nimitta and darśanabhāga would lack a supporting vastu and would thus become separate substances, meaning there would be objects outside the mind. Now, by stating that they have a support, there is no object apart from mind, and they are of one substance.