My impression before listening: it can't possibly make any difference whether possible worlds are overtly part of one's ontology, or whether counterfactual statements are handled is some other way. Our reasoning in physics acts on descriptions of the world, not on the world itself. When we say "if you extend a vacuum tube from the top of the Leaning Tower of Pisa to the ground, and drop a feather and an anvil ...", the subsequent reasoning works just as well regardless of whether or not there is a possible world in which you do so. You can even accept the entire collection of possible worlds as actual reality, say that you believe the Flying Spaghetti Monster exists in all of them and that His noodly appendage protects the tower from ever being besmirched with vacuum tubes, ever, in any possible world, and still do the physics about what would happen if the anvil and feather were dropped and not hindered by air. Nor does it have to be physics. You can talk about what minds do -- or what chemical mixtures do, or hurricanes, or populations of caterpillars preyed upon by birds -- on a crudely empirical basis, without having a sufficiently deep explanation of how they work to be able to ground it in physics, and your theory can still be a theory that correctly describes them within the scope of its applicability. Your theory will still authorize chains of reasoning that act on descriptions of the world, not on the world itself, just as physics does. So the existence of possible worlds won't matter there either. Now to see whether the lecture changes my mind.
One point: what makes your claim "if I dropped a feather and and anvil in a vacuum then they would both fall at the same speed" true is that if you did, they would. But you can make counterfactual claims that cannot be verified by the real world, like "if the laws of physics were different then..." What makes THEM true?
@@SimonCushing Implication or entailment, same as 'if these axioms are true of this bunch of things, then this theorem is also true in that model'. Alternative laws of physics (including simplifications) are applied to descriptions rather than to worlds, same as the laws that are our best available approximations to the actual ones.
love your videos Simon
Thank you
thank you, professor, for much much-needed lecture on this topic for my logic course👌
If only rasheed wallace knew there was a world where he was getting blasted in a modal logic lecture.....
I would NEVER blast Sheed! Except for that one time he threw a towel at Sabonis - but he regrets that now.
Conceivability is a worst system for metaphysics..
My impression before listening: it can't possibly make any difference whether possible worlds are overtly part of one's ontology, or whether counterfactual statements are handled is some other way. Our reasoning in physics acts on descriptions of the world, not on the world itself. When we say "if you extend a vacuum tube from the top of the Leaning Tower of Pisa to the ground, and drop a feather and an anvil ...", the subsequent reasoning works just as well regardless of whether or not there is a possible world in which you do so. You can even accept the entire collection of possible worlds as actual reality, say that you believe the Flying Spaghetti Monster exists in all of them and that His noodly appendage protects the tower from ever being besmirched with vacuum tubes, ever, in any possible world, and still do the physics about what would happen if the anvil and feather were dropped and not hindered by air. Nor does it have to be physics. You can talk about what minds do -- or what chemical mixtures do, or hurricanes, or populations of caterpillars preyed upon by birds -- on a crudely empirical basis, without having a sufficiently deep explanation of how they work to be able to ground it in physics, and your theory can still be a theory that correctly describes them within the scope of its applicability. Your theory will still authorize chains of reasoning that act on descriptions of the world, not on the world itself, just as physics does. So the existence of possible worlds won't matter there either.
Now to see whether the lecture changes my mind.
One point: what makes your claim "if I dropped a feather and and anvil in a vacuum then they would both fall at the same speed" true is that if you did, they would. But you can make counterfactual claims that cannot be verified by the real world, like "if the laws of physics were different then..." What makes THEM true?
@@SimonCushing Implication or entailment, same as 'if these axioms are true of this bunch of things, then this theorem is also true in that model'. Alternative laws of physics (including simplifications) are applied to descriptions rather than to worlds, same as the laws that are our best available approximations to the actual ones.