Modal and Intensional Logic·Rules·Lesson 2 of 5

The Modal Operators and Their Rules

Introduces the box and diamond operators formally, establishes the duality between them, and presents the core modal axioms K and T together with simple rules of necessity elimination and possibility introduction.

← What Is Modal Logic?Modal Logic: Necessity, Possibility, and Counterfactuals Formalizing Modal Arguments →

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In this lesson · 7 sections · 5 worked examples · 5 practice activities

Box and diamond are duals
Axiom K: necessity distributes over conditionals
Axiom T: necessity is truth-preserving
Axioms 4 and 5: iterating modal operators
…and 3 more

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