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14626 | In S5 matters of possibility and necessity are non-contingent [Williamson] |
Full Idea: In system S5 matters of possibility and necessity are always non-contingent. | |
From: Timothy Williamson (Modal Logic within Counterfactual Logic [2010], 3) | |
A reaction: This will be because if something is possible in one world (because it can be seen to be true in some possible world) it will be possible for all worlds (since they can all see that world in S5). |