mathworld.wolfram.com
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MathWorld is Wolfram's comprehensive online encyclopedia of mathematics, offering clear, concise explanations and definitions of mathematical topics. Its Modal Logic entry explains the modal operators, Kripke semantics, and common systems (K, T, S4, S5) with examples and links to related topics.
More resources on Modal Logic
Handbook of Modal Logic
Free excerpts and refs
Modal Logic.com
Explore the fundamentals of modal logic! Learn about necessity, possibility, and related concepts with this comprehensive website.
Stanford Encyclopedia of Philosophy: Modal Logic
Comprehensive free entry
Introduction to Modal Logic
Learn logic skills to advance your education and career with online courses delivered through edX.
Modal Logic
Learn modal logic with this comprehensive course by Wesley H. Holliday! Explore the fundamentals and applications of modal-logic.
plato.stanford.edu
Stanford Encyclopedia of Philosophy is a free, peer‑reviewed online encyclopedia of philosophy that includes detailed articles on modal logic. Each entry provides rigorous explanations, historical context, formal treatments, and extensive references, making it a key resource for learning about modal logic and related topics.