`At 13:40 26/11/04 -0500, Hal Ruhl wrote:
``What does "logically possible" mean?
`

A proposition P is logically possible, relatively to
1) a consistent set of beliefs A
2) the choice of a deduction system D (and then consistent
means "does not derive 0=1).

if the negation of P is not deductible (in D) from A.

Concerning many theories, to say that a proposition
(or a set of propositions) A is logically possible
is the same as saying that A is consistent (i.e you
cannot derive 0 = 1 from it), or saying that A has a
model (a reality, a mathematical structure) satisfying
it.

Bruno

http://iridia.ulb.ac.be/~marchal/

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