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4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / b. System K

[modern simple version, on which others build]

2 ideas

14970	Normal system K has five axioms and rules [Cresswell]
	Full Idea: Normal propositional modal logics derive from the minimal system K: wffs of PC are axioms; □(p⊃q)⊃(□p⊃□q); uniform substitution; modus ponens; necessitation (α→□α).
	From: Max J. Cresswell (Modal Logic [2001], 7.1)

9742	The system K has no accessibility conditions [Fitting/Mendelsohn]
	Full Idea: The system K has no frame conditions imposed on its accessibility relation.
	From: M Fitting/R Mendelsohn (First-Order Modal Logic [1998], 1.8)
	A reaction: The system is named K in honour of Saul Kripke.