SUO‐KIF Modal logic

SUO-KIF for the beginner

Introduction

Credited to Saul Kripke – (Kripke, S. A. A completeness theorem in modal logic. Journal of Symbolic Logic 24, 1 (1959), 1–14.)

A way to talk about formulas

• Originally just two operators: “It is possible that…” “It is necessary that...”

Since then, Modal logics covers things like:

• Deontic Logic (It is obligitory that ..., It is permitted that ..., It is forbidden that ...)
• Temporal Logic (It will always be the case that ..., It will be the case that..., It was the case that ...
• Doxastic Logic (x believes that ...)
• Epistemic Logic (x knows that ...)

In modal logic, we have a set of worlds and statements can be true in one world and not another.