This paper attempts to make sense of Dharmakīrti's conflicting statements regarding the object of valid cognition (prameya) in various parts of his works, considering in particular the claims that (i) there are two kinds of prameyas (particulars and universals), (ii) the particular alone is prameya, and (iii) what is non-existent also qualifies as prameya. It inquires into the relationship between validity (prāmān : ya), reliability (avisam : vāda) and causal efficacy (arthakriyā) and suggests that the discussion on non-existent prameyas in Pramān : aviniścaya 3 provides an alternative to an overall ''practicalist'' reading of Dharmakīrti, practicalist in the sense that pramān : as are primarily oriented toward human aims and hence bear on objects capable of fulfilling them through their causal capacities. Considering the views of Dharmakīrti's interpreters, it shows how Dharmottara (8th c.), rejecting such an alternative, strives to reconcile claim (iii) with a practicalist interpretation, while Phya pa Chos kyi seng ge (12th c.) generalizes the application of a criterion of validity superseding an arthakriyā-oriented framework by bringing to the fore the notion of ''non-opposition'' (abādhana) introduced by Dharmakīrti with regard to non-existent prameyas and suprasensorial objects.