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Full Idea
A problem with the Barcan Formula is it might be possible for there to exist a ghost, even though there in fact exists nothing that could be a ghost. There could have existed some 'extra' thing which could be a ghost.
Gist of Idea
Barcan Formula problem: there might have been a ghost, despite nothing existing which could be a ghost
Source
Theodore Sider (Logic for Philosophy [2010], 9.5.2)
Book Ref
Sider,Theodore: 'Logic for Philosophy' [OUP 2010], p.239
A Reaction
Thus when we make modal claims, do they only refer to what actually exists, or is specified in our initial domain? Can a claim enlarge the domain? Are domains 'variable'? Simple claims about what might have existed seem to be a problem.
| 17209 | A thing is contingent if nothing in its essence determines whether or not it exists [Spinoza] |
| 5039 | If non-existents are possible, their existence would replace what now exists, which cannot therefore be necessary [Leibniz] |
| 16986 | That there might have been unicorns is false; we don't know the circumstances for unicorns [Kripke] |
| 17590 | A merely possible object clearly isn't there, so that is a defective notion [Inwagen] |
| 17591 | Merely possible objects must be consistent properties, or haecceities [Inwagen] |
| 18925 | If talking donkeys are possible, something exists which could be a talking donkey [Williamson, by Cameron] |
| 15142 | Our ability to count objects across possibilities favours the Barcan formulas [Williamson] |
| 13719 | Barcan Formula problem: there might have been a ghost, despite nothing existing which could be a ghost [Sider] |
| 19037 | Are there possible objects which nothing has ever had the potentiality to produce? [Vetter] |