成唯識論演祕 3.506

3.506

想遍地故。若言想細，尋伺因麁，要有麁因方能發語，獨想不能。

[It is because] ideation pervades the stages. If you say ideation is subtle while applied and sustained thought are gross causes, there must be a gross cause to be able to issue speech; ideation alone cannot.