Module 02 — The JTB Problem
In 1963, Edmund Gettier showed in three pages that justified true belief is not sufficient for knowledge. Walk through the cases, then test every proposed fix — and watch each one break.
The classical analysis of knowledge — dating to Plato's Meno — defines knowledge as justified true belief (JTB): S knows P iff P is true, S believes P, and S has adequate justification for believing P. This account dominated analytic epistemology through the mid-20th century.
Gettier's 1963 paper constructed two cases where all three JTB conditions are met, yet the subject intuitively does not have knowledge. The cases share a common structure: a subject reasons validly from a justified false belief to a conclusion that turns out to be true — but for entirely unrelated reasons. The truth and the justification come apart.
Step through each case below, then use the Solution Tester to see how philosophers have tried — and mostly failed — to patch the JTB account.
Select a proposed solution. See how it handles both Gettier cases, then see the variant case that breaks it.
Click any row to jump to that solution's analysis. Every proposed fix handles the original cases but breaks on a variant.