Among challenges to internalism, the Gettier problem has pride of place. Four decades of discussion and analysis have produced no consensus on the problem itself, but the externalist response has been (not surprisingly) to tout it as evidence that internalism is seriously flawed. Alvin Plantinga, in particular, has argued that the Gettier problem is not just a minor conundrum requiring us to ‘‘tweak’’ the traditional TJB definition of knowledge but rather a sign that external factors regarding proper function are constitutive of the deepest and most important epistemic concepts.