The locus classicus for Kumārila’s argument here is verse 47 of the codanā sūtra chapter of the Ślokavārttika: “It should be understood that all pramāṇas’ have the property of being pramāṇas intrinsically; for a capacity not already existing by itself (svataḥ) cannot be produced by anything else.” (All of the passages given here from Kumārila and his commentators can be found in Arnold 2005, 57–114.) The argument Kumārila concisely expresses here in verse form is straightforward but compelling