syād etat vijñānahetave 'pi pramāṇāpramānasādhāraṇāḥ tat kathaṃ vijñānahetumātrapratibaddhaṃ prāmāṇyaṃ syāt
[One might object:] Since the causes of cognition are common to both valid and invalid cognitions, how could validity be dependent merely on [something's] being a cause of cognition?