Re: Recursivity vs. Provability


Charlie-Boo wrote:
>
> But there are properties of truth that hold for all models, e.g. if P
> is true then ~P is false. These we can rely on.
>
> I had considered also asking the question of what general properties
of
> truth are there, and can we show the relationships among them, but
> didn't want to mix the 2 questions. However, now that I have, here
are
> a few:
>
> 1. If P is true then ~P is false.
> 2. If P is false then ~P is true.
> 3. P has the same value as ~~P.
> 4. P is either true or false.
> 5. P is not both true and false.
>

Not all of these are the case in some multi-valued formal logics, or
even informal intuitionist logic.

.

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