Non-Alethic Entailment

When discussing types like Grice's

Post the letter or burn it!

----

we have to distinguish that from Grice's serious efforts to stimulate (or simulate) the common-ground status of things like

"There is an intruder and arrest him!"

-----

(In WoW:Presupp. and Conv. Impl.). There he notes that in a way, the pragmatic expansion of the logical form does introduce an element of 'stating'.

--- i.e. the utterer of

"Arrest the intruder!"

presupposes or conversationally implicates that (he states) that there is an intruder.

In the case of

"Post the letter! Therefore, Post the letter or burn it!"

we can speak of non-alethic entailment WITHOUT obvious recourse to this pragmatic expansion of the logical form. Non-alethic entailment is NOT presupposed alethic entailment. Or something.

Nothing in the definition of entailment by Moore entails the thing is merely alethic (-- but can be defined in terms of 'validity' in general -- Ross's term -- or satsifaction-preserving features of satisfaction-functional operators like 'or').