more from M Fitting/R Mendelsohn

### Single Idea 9740

#### [catalogued under 4. Formal Logic / D. Modal Logic ML / 2. Tools of Modal Logic / c. Derivation rules of ML]

Full Idea

If a proposition is possibly true in a world, then it is also true in some world which is accessible from that world. That is: Γ ||- ◊X ↔ for some Δ ∈ G, ΓRΔ then Δ ||- X.

Gist of Idea

If a proposition is possibly true in a world, it is true in some world accessible from that world

Source

M Fitting/R Mendelsohn (First-Order Modal Logic [1998], 1.6)

Book Reference

Fitting,M/Mendelsohn,R: 'First-Order Modal Logic' [Synthese 1998], p.13