The warrant and proper function approach argues that religious belief can possess warrant—that property which converts true belief into knowledge—when cognitive faculties function properly in an appropriate environment according to a design plan aimed at truth. This epistemological framework contends that if humans possess a sensus divinitatis or similar God-detecting faculty operating correctly, theistic belief can be warranted without requiring evidential support or argumentation. The approach challenges classical foundationalism's demand that religious beliefs require propositional evidence or inference from more basic beliefs, proposing instead that belief in God can be as warranted as perceptual or memory beliefs when arising from properly functioning cognitive mechanisms.
Alvin Plantinga developed this approach comprehensively in his trilogy: Warrant: The Current Debate (1993), Warrant and Proper Function (1993), and Warranted Christian Belief (2000). Building on Thomas Reid's common sense philosophy and Calvin's sensus divinitatis, Plantinga argues that warrant requires: (1) proper function of cognitive faculties, (2) an appropriate epistemic environment, (3) faculties aimed at truth, and (4) reliability in that environment. Michael Bergmann's Justification without Awareness (2006) extends this externalist framework, while William Alston's Perceiving God (1991) applies similar principles to religious experience. C. Stephen Evans in Natural Signs and Knowledge of God (2010) develops the notion of natural signs as triggers for properly basic theistic beliefs.
Critics raise several objections to this approach. The Great Pumpkin objection, formulated by Michael Martin and Keith Parsons, argues that any belief system could claim warrant through alleged proper function, rendering the criterion vacuous. Richard Feldman and other evidentialists contend that the approach licenses epistemic irresponsibility by abandoning evidential requirements. The evolutionary debunking argument, advanced by Paul Griffiths and Wilkins, suggests that religious faculties evolved for survival rather than truth, undermining their reliability. Defenders respond that: (1) not all belief-forming mechanisms are equally plausible given our total evidence, (2) proper function provides objective constraints absent in pure fideism, and (3) evolutionary arguments equally threaten naturalistic accounts of reason itself.
This formulation differs from other reformed epistemology approaches in its specific focus on warrant conditions. While Plantinga's Model encompasses the entire A/C model including sin's noetic effects and the internal instigation of the Holy Spirit, warrant and proper function concentrates on the general epistemological framework. Unlike properly basic beliefs which emphasizes the foundational status of theistic belief, this approach details the externalist conditions for warrant. It provides the theoretical apparatus for responding to the Great Pumpkin objection by specifying objective criteria for proper function.