Griceian Letters Sent From the Heart

From Harman's online review of Grice's "Aspects of reason" (Harman thinks he can correct Grice because he has his own "Principles of reasoning" out! :)).

"Consider the principle that an alethic disjunction is true just in case one of its disjuncts is true. Grice proposes to extend that to the principle that a disjunction of any sort is satisfactory just in case one of its disjuncts is satisfactory. This
implies that if “Mail these letters!” is satisfactory, so is “Mail these letters
or burn them!”"

Harman:

"Consider
the principle that an alethic disjunction is true just in case one of its disjuncts
is true."

This is actually what Grice (Vacuous Names, and Jones knows of this) calls

(+, v)

i.e. it is the introduction of 'or'. And surely it would be otiose to think that 'or' has two senses: one in indicative discourse, and one in imperative discourse.

---

Surely the introduction rules in System G have to be generalised for denominational types, /- and ! -- so that they cover any mode. Where any mode may be symbolised by "*".

Harman goes on:

"Grice proposes to extend that to the principle that a disjunction of
any sort is satisfactory just in case one of its disjuncts is satisfactory."

---- on the principled assumption that connectors are satisfaction-functional, rather than merely truth-functional.

---- (or alethic functional).

Harman spots something like a Megarian paradox, with which Philo was well aware but never felt the need to change his views (I think Harman's book is "Views in change"?).

Harman:

"This implies that if “Mail these letters!” is satisfactory, so is “Mail these letters or burn them!”"

---

And it is. Ross failed to see this back in 1944, because -- we don't know much about Ross. But R. M. Hare criticised Kenny for making too much of a fuss out of a simple conversational implicatum.

Harman/Davidson (or Davidson/Harman) were the first to reprint Grice's second essay on implicatum (I mean the second William James lecture) back in 1975, so he should know, and does!

---

"If (1) is satisfactory, so is (2)

(1) Mail these letters!
(2) [Therefore,] Mail these letters or burn them!

----

And it is.

"Mail those letters or burn them!" is satisfactory. Only that as Kenny notes, it is not satisfactory-satisfactory. The fiat Fiat(pvq) is not one that would utter when only Fiat(p) is _intended_.

"Mail those letters!" is satisfied by the addressee mailing the letters.

"Mail those letters or burn them!" is satisfied by the addressee either mailing those letters or burning them.

Note that Grice is NOT talking of 'conjunction'.
Just 'disjunction' -- and introduction of it, further.

And so on.

Hare wisely pointed out to Grice's "Causal theory of perception", where the example:

"My wife is in the kitchen OR in the bathroom" was analysed in truth-functional terms. Indeed, here the point of 'strength' or informativeness is very apt because one (the disjunct) follows from the statement (or order) containing ONE of the disjuncts. (Informativeness defined in terms of alethic and non-alethic entailment).