- Contemporary messages sorted: [ by date ] [ by thread ] [ by subject ] [ by author ] [ by messages with attachments ]

From: Jesse Mazer <lasermazer.domain.name.hidden>

Date: Fri, 23 Jul 2004 16:58:14 -0400

Bruno Marchal wrote:

*>All right. But modal logic are (traditionaly) extension of classical logic,
*

*>so that causal implication, or >natural language entailment, when study
*

*>mathematically are generally defined through modalities + >"material
*

*>implication".
*

*>
*

*>So in a sense, you confuse yourself by premature anticipation.
*

Well, I guess "in every possible world where X is true, Y is true also" can

only be false if there's a possible world where the classical logical

statement "X -> Y" is false (because in that possible world, X is true but Y

is false). So perhaps the possible-world statement would be equivalent to

the modal-logic statement "it is necessarily true that X->Y"--would this be

an example of modal logics "extending" classical logic? In any case, in

classical logic X -> Y can only be false if X is true in *our* world,

whereas the possible-world version of "if X then Y" does not require that X

is true in our world, although it must be true in some possible world. And

like I said, I think the possible-world statement more accurately captures

the meaning of the natural-language statement.

Jesse

Received on Fri Jul 23 2004 - 17:04:43 PDT

Date: Fri, 23 Jul 2004 16:58:14 -0400

Bruno Marchal wrote:

Well, I guess "in every possible world where X is true, Y is true also" can

only be false if there's a possible world where the classical logical

statement "X -> Y" is false (because in that possible world, X is true but Y

is false). So perhaps the possible-world statement would be equivalent to

the modal-logic statement "it is necessarily true that X->Y"--would this be

an example of modal logics "extending" classical logic? In any case, in

classical logic X -> Y can only be false if X is true in *our* world,

whereas the possible-world version of "if X then Y" does not require that X

is true in our world, although it must be true in some possible world. And

like I said, I think the possible-world statement more accurately captures

the meaning of the natural-language statement.

Jesse

Received on Fri Jul 23 2004 - 17:04:43 PDT

*
This archive was generated by hypermail 2.3.0
: Fri Feb 16 2018 - 13:20:09 PST
*