Why Being Necessary Really Is Not the Same As Being Not Possibly Not

Abstract

© 2015, Springer Science+Business Media Dordrecht. In standard modal logic, □ ≡ ∼◊ ∼ and ◊ ≡ ∼□∼. I will, first, examine why in tense-logic, Arthur Prior thinks that ∼ ◊ ∼ is weaker than □ and ∼ □ ∼ is weaker than ◊. I will, then, examine whether there are similar motivations in modal logic to take ∼ ◊ ∼ to be weaker than □ and ∼ □ ∼ to be weaker than ◊. The upshot will be that, just as certain metaphysical views within the philosophy of time (e.g., Presentism) motivate one to deny the standard tense equivalences, certain metaphysical views within the metaphysics of modality (e.g., Contingentism, nonmodalism) motivate one to deny the standard modal equivalences.