I’m reading a chapter from David Lewis’s counterfactuals. He says something which I’m confused about, wondering if any of you guys can explain what he's saying...
“ We might take…. ‘Possibly P’ [to mean] that P is a consistent sentence… If a consistent sentence is one that comes out true under some assignment of extensions to the nonlogical vocabulary, then the theory is incorrect: some assignments of extensions are impossible, for instance one that assigns overlapping extensions to the English terms ‘pig’ and ‘sheep’.”
I’ve taken logic so I know what he means by assigning extensions to nonlogical terms but I’m failing to see how some assignments of extensions are impossible. Some extensions are impossible (e.g. the round square), but I'm failing to see how some assignments of extensions to nonlogical terms (given that the extensions exist) is impossible.
Thanks for any answers :))