Combining Texts

Ideas for 'fragments/reports', 'Four Dimensionalism' and 'Mere Possibilities'

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2 ideas

4. Formal Logic / D. Modal Logic ML / 3. Modal Logic Systems / a. Systems of modal logic

16468	Non-S5 can talk of contingent or necessary necessities [Stalnaker]
	Full Idea: One can make sense of necessary versus contingent necessities in a non-S5 modal semantics.
	From: Robert C. Stalnaker (Mere Possibilities [2012], 4.3 n17)
	A reaction: In S5 □φ → □□φ, so all necessities are necessary. Does it make any sense to say 'I suppose this might have been necessarily true'?

4. Formal Logic / F. Set Theory ST / 4. Axioms for Sets / b. Axiom of Extensionality I

16449	In modal set theory, sets only exist in a possible world if that world contains all of its members [Stalnaker]
	Full Idea: One principle of modal set theory should be uncontroversial: a set exists in a given possible world if and only if all of its members exist at that world.
	From: Robert C. Stalnaker (Mere Possibilities [2012], 2.4)
	A reaction: Does this mean there can be no set containing all of my ancestors and future descendants? In no world can we coexist.