Knowledge, Justification, and Adequate Reasons

TL;DR

This paper explores the concept of knowledge as justified true belief, introducing a logic of reason-based belief to analyze adequacy of reasons and compare internalist and externalist views, highlighting implications for Gettier cases.

Contribution

It develops a propositional logic of reason-based belief with axioms for adequacy, and applies it to distinguish internalist and externalist notions of justification in knowledge.

Findings

Gettier cases challenge internalist JTB but not externalist JTB.

The framework supports quantification over reasons.

The approach suggests knowledge involves only some adequate reasons.

Abstract

Is knowledge definable as justified true belief ("JTB")? We argue that one can legitimately answer positively or negatively, depending on whether or not one's true belief is justified by what we call adequate reasons. To facilitate our argument we introduce a simple propositional logic of reason-based belief, and give an axiomatic characterization of the notion of adequacy for reasons. We show that this logic is sufficiently flexible to accommodate various useful features, including quantification over reasons. We use our framework to contrast two notions of JTB: one internalist, the other externalist. We argue that Gettier cases essentially challenge the internalist notion but not the externalist one. Our approach commits us to a form of infallibilism about knowledge, but it also leaves us with a puzzle, namely whether knowledge involves the possession of only adequate reasons, or leaves room for some inadequate reasons. We favor the latter position, which reflects a milder and more realistic version of infallibilism.