more from Brian Ellis

### Single Idea 13604

#### [catalogued under 4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / h. System S5]

Full Idea

The logic of real possibilities and necessities is just S5. This is because the accessibility relation for real possibilities links possible worlds of the same natural kind, which is an equivalence class.

Gist of Idea

Real possibility and necessity has the logic of S5, which links equivalence classes of worlds of the same kind

Source

Brian Ellis (Scientific Essentialism [2001], 7.06)

Book Reference

Ellis,Brian: 'Scientific Essentialism' [CUP 2007], p.242

A Reaction

Most people, except Nathan Salmon, agree with this. With full accessibility, you seem to take epistemological problems out of the system, and just focus on reality.