more from David M. Armstrong

### Single Idea 15544

#### [catalogued under 4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / g. System S4]

Full Idea

Armstrong says what is actual (namely a certain roster of universals) might have been impossible. Hence his modal logic is S4, without the 'Brouwersche Axiom'.

Gist of Idea

If what is actual might have been impossible, we need S4 modal logic

Source

report of David M. Armstrong (A Theory of Universals [1978]) by David Lewis - Armstrong on combinatorial possibility 'The demand'

Book Reference

Lewis,David: 'Papers in Metaphysics and Epistemology' [CUP 1999], p.202

A Reaction

So p would imply possibly-not-possibly-p.