On 25 Feb 2014, at 18:44, meekerdb wrote:

On 2/25/2014 7:15 AM, Bruno Marchal wrote:

On 23 Feb 2014, at 20:38, meekerdb wrote:

On 2/23/2014 4:35 AM, David Nyman wrote:
Not "my" consciousness, no. I'm just suggesting that CTM ultimately relies on some transcendent notion of perspective itself. IOW, the sensible world is conceived as the resultant of the inter-subjective agreement of its possible observers, each of which discovers itself to be centred in some perspective.

Is the sensible world of *possible* observers supposed to include the whole world. I'm always suspicious of the word "possible". Does it refer to chance, i.e. many events were possible, I might have had coffee instead of tea this morning, but only a few are actual? Does it refer to anything not prohibited by (our best theory of) physics: It's possible a meteorite might strike my house? Or is it anything not entailing a contradiction: X and not X?

Possible in the large sense, is the diamond of the modal logic.

But <> is just a symbol that we use with certain rules of inference. To be applied it requires some interpretation.

That's the point.

Mathematical semantics provides then the math for describing a lot of them, including sound and complete in their characterization of some modal theory.





There are as many notions of possibility than there are modal logics, and there are many.

I appreciate that you put in your enumeration the "possible" in the sense of the "consistent" (not entailing A & ~A, or not entailing f).

David used "possible observers" as part of a definition. I don't know what it would mean for an observer to not entail f. So I think he had some other meaning (nomological) in mind. But in that case his definition is somewhat circular.

I will interview correct rational machine, and I will say that a machine believes A is she asserts A.
To say that they do not assert f means that they are consistent.

Bruno




Brent


That one, consistency, can be defined in arithmetic for all arithmetically correct machine(~beweisbar('~(0=0)')), and it happens also that such a definition entails different logics for the "philosophical" or "physical" variant of it, and this choose the different modal logics from machines self-references.




Bruno


PS my p-time seems to be delayed, I am still in the 23 february, gosh!


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



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