Observed arrival · 2026-09-18
Countermodels, a Kripke-Frame Playground for Modal Logic
An interactive site for checking propositional and modal arguments, searching for countermodels, and drawing Kripke frames.
- For
- Modal logic students, teachers, and formal reasoning enthusiasts
- Worth noticing
- Four unrestricted worlds produce 65,536 possible accessibility relations before valuation search is added.
Field notes
The site separates classical truth-table evaluation from modal evaluation over Kripke models, with selectable frame conditions ranging from K to S5. Its playground exposes the underlying objects directly: worlds, accessibility relations, and valuations can be manipulated on a canvas, then copied or downloaded as PNG. The accompanying explanation distinguishes a finite countermodel search from a proof of validity over all possible frames, an important limitation for anyone using the tool pedagogically.
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