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I got confused by the way different people use language in the context of physicalism.

In particular, Kripke seems to equate "necessary truths" with something that is true in all possible worlds. Is this a metaphysical necessity, because there is some invariant mechanism (metaphysical physicalism)?

Also, I have seen people (I think it was Kim) claim that something can be nomologically true in any possible worlds. This seems like a contradiction to me, in the following sense.

Wikipedia has the following definition;

nomological denotes something resembling general laws, especially laws that lack logical necessity or theoretical underpinnings; they just are.

So if there is no logical necessity, if it's just brute fact, how can it be necessarily true in all possible worlds? I'd say the opposite, namely that a nomological identity is one that is observed to hold but which may not hold in all possible worlds.

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  • Kripke's necessity is indeed metaphysical, I am not sure what "invariant mechanism" means. Metaphysical necessity entails nomological necessity, but not vice versa. Please spell out what seems to be a contradiction.
    – Conifold
    Jun 10 '19 at 21:10
  • @Conifold I elaborated a little.
    – Michael Angelo
    Jun 11 '19 at 11:33
  • Do you have a reference for where (Jaegwon?) Kim said something like this? Without context, it doesn't seem right to me either. Nomologically possible worlds are a subset of metaphysically possible worlds, which are a subset of logically possible worlds. Nomological truths in our world might not be nomological or true in other metaphysically possible worlds.
    – Adam Sharpe
    Jun 11 '19 at 14:32
  • To be necessarily true just means to be true in all possible worlds, Wikipedia is not a good source for precise definitions. See e.g. Nomological Necessity on philpapers.org:"Some philosophers first give a theory of what laws of nature are and then can say on that basis that events happen with nomological necessity when they happen because of the laws. Other philosophers take nomological necessity to be basic and define law statements in terms of nomologically necessary relations in nature."
    – Conifold
    Jun 11 '19 at 15:00
  • @Conifold I see. Under this interpretation, what is the difference between nomological and metaphysical necessity? Am I right to state that for example 'it is a metaphysical necessity that $H^2O$ is water (ontological) and it is nomologically, but not metaphysically necessary that young stars do mainly hydrogen fusion because the laws of nature are such that the nuclear binding energies are such and such while in another universe they might be different?
    – Michael Angelo
    Jun 11 '19 at 15:31

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