more from John P. Burgess

Single Idea 15419

[catalogued under 10. Modality / A. Necessity / 6. Logical Necessity]

Full Idea

To the extent that there is any conventional wisdom about the question, it is that S5 is correct for alethic logical modality, and S4 correct for apodictic logical modality.


'Alethic' concerns truth; 'apodictic' concerns proof

Gist of Idea

General consensus is S5 for logical modality of validity, and S4 for proof


John P. Burgess (Philosophical Logic [2009], 3.8)

Book Reference

Burgess,John P.: 'Philosophical Logic' [Princeton 2009], p.65

A Reaction

In classical logic these coincide, so presumably one should use the minimum system to do the job, which is S4 (?).

Related Idea

Idea 15417 Logical necessity has two sides - validity and demonstrability - which coincide in classical logic [Burgess]