Full Idea
Modality in the actual world is the import of the Barcan formula, and there are good reasons for accepting the Barcan formula.
Gist of Idea
The plausible Barcan formula implies modality in the actual world
Source
Alexander Bird (Nature's Metaphysics [2007], 1.2)
Book Reference
Bird,Alexander: 'Nature's Metaphysics' [OUP 2007], p.6
A Reaction
If you thought logic was irrelevant to metaphysics, this should make you think twice.