Full Idea
The Converse Barcan Formula reads □∀αφ→∀α□φ (or an equivalent using ◊).
Gist of Idea
Converse Barcan Formula: □∀αφ→∀α□φ
Source
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.