Full Idea
Lewis equates knowing which world is actual with knowing which world one is in.
Gist of Idea
The actual world is just the world you are in
Source
report of David Lewis (Attitudes De Dicto and De Se [1979]) by Cappelen,H/Dever,Josh - The Inessential Indexical 05.1
Book Reference
Cappelen,H/Dever,J: 'The Inessential Indexical' [OUP 2013], p.89
A Reaction
[This view is not, of course, Actualism, but an alternative treatment of actuality, within a multitude of possibilities].