more from M Fitting/R Mendelsohn

### Single Idea 9739

#### [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 necessarily true in a world, then it is also true in all worlds which are accessible from that world. That is: Γ ||- □X ↔ for every Δ ∈ G, if ΓRΔ then Δ ||- X.

Gist of Idea

If a proposition is necessarily true in a world, it is true in all worlds 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