俱舍論記 30.108

30.108

「必定應信至理不成故」者，勝論標宗，勸論主信。必定應信我體實有，以有念等德句義故。夫德必依實句義故，我是實句，為彼念等德句所依，明知有體。我實若無，何成依止？實句九中念等依我，念等依餘地等八實，理不成故。

"One must definitely believe [...] because the principle is not established": this is the Vaiśeṣika stating their tenet and urging the master of the treatise to believe it. One must definitely believe that the substance of the self really exists, because there is the category of quality such as mindfulness. Now, qualities must depend on the category of substance; the self is a substance and serves as the support for those qualities such as mindfulness, so clearly it has real existence. If the substance of the self did not exist, what could serve as the support? Among the nine substances, mindfulness and so forth depend on the self; for mindfulness and so forth to depend on the other eight substances such as earth is not logically established.