Full Idea
Every argument I am aware of against impossible worlds confuses ways for things to be with ways things might have been, or worse, confuses ways things cannot be with ways for things to be that cannot exist - or worse yet, commits both errors.
Gist of Idea
Denial of impossible worlds involves two different confusions
Source
Nathan Salmon (The Logic of What Might Have Been [1989], III)
Book Reference
Salmon,Nathan: 'Metaphysics, Mathematics and Meaning' [OUP 2005], p.138
A Reaction
He is claiming that 'ways for things to be' allows impossible worlds, whereas 'ways things might have been' appears not to. (I think! Read the paragraph yourself!)
Related Idea
Idea 14687 Without impossible worlds, how things might have been is the only way for things to be [Salmon,N]