八識規矩補註 2.30

2.30

It also says that sentient beings transmigrate through the five destinies and four modes of birth; if this eighth consciousness did not exist, the substance of those destinies and births could not exist. That is to say, only by being real, constant, pervasive, and unmixed—being endowed with these four characteristics—can genuine destinies and births be established. If it were that which is induced by the karma of the first five consciousnesses, it would not pervade the destinies and births, because in the formless realm these are entirely absent; although what is induced by karma of the manovijñāna pervades the destinies and births, it is not constant; only the maturation mind and its associated caittas are endowed with the four characteristics, and are therefore the genuine destinies and births; apart from this eighth consciousness, this mind and its caittas cannot logically be established. This explains the two characters "destinies and births" (qu sheng) to prove that the eighth is the substance of the destinies and births. Furthermore, the sūtra states that the physical body with material faculties possesses appropriation; if this consciousness did not exist, that which can appropriate could not exist. This mind that can appropriate is solely the maturation mind; the evolving consciousnesses such as the eye [consciousness] do not possess such a function. Furthermore, the sūtra states that life span, warmth, and consciousness mutually support each other to abide in continuous succession; if this consciousness did not exist, a consciousness able to maintain life span and warmth and cause them to abide for a long time could not exist. This is because the evolving consciousnesses have interruptions and fluctuations, like sounds and the wind, lacking the function of constant maintenance, and cannot be established as the consciousness that maintains life span and warmth; only the maturation [consciousness] has the function of constant maintenance, so it can be established as the consciousness maintaining life span and warmth: this explains the meaning of the character "consciousness" (shi). Encompassing the various meanings above, this explains the next line: "the realms and births, possessing appropriated [faculties], consciousness."