more from Theodore Sider

Single Idea 13720

[catalogued under 4. Formal Logic / D. Modal Logic ML / 7. Barcan Formula]

Full Idea

The Converse Barcan Formula reads □∀αφ→∀α□φ (or an equivalent using ◊).

Gist of Idea

Converse Barcan Formula: □∀αφ→∀α□φ


Theodore Sider (Logic for Philosophy [2010], 9.5.2)

Book Reference

Sider,Theodore: 'Logic for Philosophy' [OUP 2010], p.240

A Reaction

I would read that as 'if all the αs happen to be φ, then αs have to be φ'. Put like that, I would have thought that it was obviously false. Sider points out that some new object could turn up which isn't φ.