Our usual understanding of possible worlds are simply references to any possible state of affairs. They have no ontic grounding or actuality. It’s a semantic tool. However, there are those who treat possible worlds as actual. (The world actual becomes very fuzzy in modal realism). Philosopher David Lewis is the leading proponent of modal realism (Lewisian modal realism) and he has developed six essential doctrines to understanding modal realism:
- Possible worlds exist–they are just as real as our world
- Possible worlds are the same sort of things as our world–they differ in content, not in kind
- Possible worlds cannot be reduced to something more basic–they are irreducible entities in their own right
- Actuality is indexical. When we distinguish our world from other possible worlds by claiming that it alone is actual, we mean only that it is our world
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