Empiricism and Logic

[Darth Wong]

I would prefer to say that we only view the rules of logic as being superior to other man-made philosophical rulesets because they are useful, ie- you can say that if fact A is true, and conclusion B can be deduced from fact A using the rules of logic, then conclusion B is true. In reality.

In an irrational universe, that would not be the case. So even if one devised a system of logic, it would be a largely meaningless set of rules, as arbitrary as the rules of a card game.

The largest problem with this objection is its underlying assumption that rules which seem very odd to us are necessarily irrational. Consider a primitive's impression: the temperature changes significantly and spontaneously all the time. Light spontaneously pours from a small region of the sky which moves about. Water disappears when standing in the open. Other times it just falls from the sky. Dust motes dance around randomly in the air. And what's up with this 'fire' thing?

Compared to those highly real phenomena, rocks changing size spontaneously seems fairly tame.

You understand that the size-changing rock was just used as an example of a hypothetical universe that lacks consistent behaviour, right? You miss the point when you argue that maybe there are logical rules governing this size-change behaviour.

[petesampras]

you can say that if fact A is true, and conclusion B can be deduced from fact A using the rules of logic, then conclusion B is true. In reality.

I really do not think that it is correct to think of this being dependant on the universe itself following some sort of order. If fact A is true and logically fact B derives from fact A, then fact A must be true regardless of the universes rules. The reason for this is that, if you can derives fact B from fact A via logic, then fact(s) A must contain all the empircal evidence needed to prove B already. Logic, in it's strictist definitions, cannot generate actual predictions about the universe, it can only rewrite statements.

It is easiest to see this with a simple example.

Premises - A and (A->B)

We can use the rules of logic to derive B from this, but this is not going to tell us anything about the world we didn't already know. To assume that A-> B you are assuming that whenever A is true B is true. You must, therefore, already believe (empirically or via faith or whatever) that B is true in this case - via the definition of A->B. The rules of logic let you restate what you already believe in new ways, but they cannot generate genuinely new knowledge about the universe.

In an 'irrational' universe logic would be completely useless, but it would still be just as valid as in this universe. It would just be impossible to ever say that A->B about anything with any confidence.

[drachefly]

You understand that the size-changing rock was just used as an example of a hypothetical universe that lacks consistent behaviour, right? You miss the point when you argue that maybe there are logical rules governing this size-change behaviour.

I do understand. My point was that if you can't tell whether the universe is rational or not, what use is including it as a criterion for the utility of an abstraction?

[drachefly]

I did not here mean that our minds necessarily use logic to think; I meant that our minds can be described logically: at any one moment, you are not both thinking about cats and not thinking about cats (or whatever); if you define a symbol to mean one thing, it does not also mean something else (though it is perfectly possible to think you had defined a symbol well, but be wrong); and so on.

If you wish to simply re-affirm the law of non-contradiction, you are of course free to do so, as it can always be rescued after making sufficiently many distinctions, but this doesn't mean it has any more a priori import beyond the fact that this law is present in some systems of logic.

In the earlier debate over this I had been a part of, the assumption of the law of non-contradiction was indeed the main point at hand.
My strategy was to point out that you don't need it as an assumption.

A proposition like "I am in a house right now" has an unclear truth value when one is stepping through the door.

This would fall into the category of 'statements that are not propositions' that I alluded to. In this case, 'in' and 'now' are problematic.

As you are a physicist, I wonder whether you are ever bothered by the Everett many-world interpretation of quantum mechanics.

Everything else but that bothers me. Maybe not in Everett's version.

One can say that such things are not 'really' part of our ontology, and that we merely play a kind of language-game when we engage in such talk, but there always seemed to me something deeply unsatisfying in such "we pretend they're there but they're not" moves.

If you're taking that interpretation, then they are there, no pretending involved. You just don't get to see most of them.

.. I do not see the connection to counterfactuals. Also, as for the ad-hoc principles, the MW interpretation is just quantum mechanics when looked at with no sugar-coating.

Theories that require many layers of ad hoc hypotheses and distinctions are less preferable to those that do not. That's why I simply can't buy into an empathic affirmation of the rules of logic.

The rules are just what you define. The question I was working on was whether there was any subject matter it could describe.

[Rye]

What makes you think we would have been able to devise logic in an illogical universe?

In an irrational universe, there's not going to be any reason why you can't concoct logic, for instance, an irrational universe might happen to look consistent and relatively rational for several billion years, then revert to a gigantic rotating clown universe populated by sharpened spheres. Plus in such a universe, all memory, observation, ideas and sense of self would be subject to the instantaneous arbitrary creation and destruction inherent in such a state of existence, you could get this exact moment in time of this universe in that one, complete with memories, etc, the concept of logic would exist for that moment before we all become a giant inverted banana.