Philosopher working in Melbourne, Australia. My book Meaning and Metaphysical Necessity is forthcoming in June 2022 with Routledge.
Why is it OK to use deduction theorem, though? In standard modal logics like K and S5 the deduction theorem doesn't hold (otherwise you could assume P, use necessitation to get []P, and then use deduction theorem to get P -> []P as a theorem).
Why is it OK to use deduction theorem, though? In standard modal logics like K and S5 the deduction theorem doesn't hold (otherwise you could assume P, use necessitation to get []P, and then use deduction theorem to get P -> []P as a theorem).