 Following Dharmakīrti, Tibetan epistemologists restrict the number of reliable cognitions to two sorts: perception and inference. The first is defined as “non-erroneous and devoid of conceptualization,” the second as the “understanding coming from a triply characterized logical reason.” Both share the status of being “reliable cognitions” (tshad ma), a status that Dharmakīrti associatedin his Pramāṇavārttika with the characteristics of being (1) “non-belying” and (2) “revealing an unknown object.” In addition to a prolongation of the commentarial dispute on the verses in which these characteristics are given, a notable confrontation is found in the Tibetan tradition between two models that can be distinguished in view of the understanding of perception that they entail: (a) a model in which perception retains a passive status insofar as, being devoid of conceptualization, it cannot itself achieve a determination of its object, and (b) a model that seeks to give a more active role to perception without however stepping back on its characterization as “non-conceptual.” Two versions of the “active perception” model are found: an “indirectly active perception” model and an innovative “directly active perception” model.