# [FOM] A minor issue in modal logic

Michael Carroll mcarroll at pobox.com
Mon Jul 5 00:53:22 EDT 2010

Richard Heck wrote:

> Of course, one might sensibly argue that any reasonable notion of
> necessity must validate "N\phi --> \phi" and so argue that any modal
> logic modelling any reasonable notion of necessity must have only models
> in which the accessibility relation is reflexive. But that is a
> substantive---i.e., not purely logical---claim.

I'm sorry but I fail to see how that differs from :

"One might sensibly argue that any reasonable notion of conjunction must
validate "((A & B) -> (B & A))", so that any logic modeling any reasonable
notion of conjunction must have only models in which conjunction is
commutative. But that is a substantive -- i.e., not purely logical --
claim."

Michael Carroll