Folk Epistemology and Epistemic Closure

Joint work with Alex Wiegmann:

Epistemic Closure and Folk Epistemology (Penultimate Draft, January 2017)

Abstract: The principle of closure of knowledge under known entailment – also called “epistemic closure” – states that if someone knows some proposition P and also knows that P entails Q, she knows Q as well. This principle is considered to be highly intuitively and plays an important role in many epistemological debates. However, only recently closure was put to the empirical test. Turri (2015a) claims that his data showed that closure is not the highly plausible principle that the epistemological literature assumes it to be. We disagree with this diagnosis. In two experiments we manipulated the strength of entailment of two propositions and found that the stronger the entailment was, the lower was the proportion of subjects who violated closure, indicating that folk knowledge ascriptions are sensitive to entailment. We discuss Turri’s and our findings as well as methodological issues of empirically testing closure, and conclude that closure is a principle of folk epistemology.