I put out an invitation to put up an argument for the existence of possibility that is distinct from logical possibility.

I don't see that you did that.

LOL. You take your role as historian pretty seriously. Thanks.

If A and B have the same properties, A=B. Show what properties physical possibilities have that logical possibilities don't or vice versa.

. . . and he won't even answer a simple question. What is wrong with people who frequent message boards like this?

If A and B have the same properties, A=B. Show what properties physical possibilities have that logical possibilities don't or vice versa. — Mongrel

Some empirical proposition P is physically impossible if its truth is ruled out by physical law. But if the physical law is contingent, then the truth of the proposition P is logically possible. It could have been true if the physical laws had been different. Only if all actual physical laws are deemed to be logically necessary does the logical possibility of P entail the physical possibility of P. This would mean, of course, that the truth of physical laws could in principle be inferred from pure logical analysis, which few philosophers believe to be the case.

So if physical law is necessary, then the set of physical possibilities has the same members as the set of logical possibilities.

Leibniz knew his CIC (which you mentioned earlier) threatened the existence of free-will. We know this because he explicitly described the problem. He came up with a number of methods for rescuing free will without abandoning his central philosophy. If you'd like to discuss those methods and how one of them might amount to basing free will on what we call logical possibility, you can start a thread on it and I'll join you in the discussion. You probably already noticed that the SEP isn't sufficient for getting the whole picture on Leibniz. I've appreciated Nicholas Jolley's book.

Neither of you offered a reason to allow some kind of possibility that is distinct from logical possibility. — Mongrel

Do you think there is a relationship between physical possibility and logical possibility? If so, what is it?

The invitation was more to make the term "physical possibility" meaningful by offering a persuasive reason to believe there is such a thing. It looked to me that previously all that was offered was that "this is the way it's normally thought...."

When a photon travels towards a double-slit, is it logically possible that it goes through both slits?

So if physical law is necessary, then the set of physical possibilities has the same members as the set of logical possibilities. Is that what you're saying? — Mongrel

Rather, only if universally quantified statements that express physical laws are logically necessary does logical possibility entail physical possibility. But it is commonly regarded that the laws of physics aren't logical laws, and hence that something can be physically necessary that isn't logically necessary. You have offered no reason to think that the laws of physics are logically necessary.

When a photon travels towards a double-slit, is it logically possible that it goes through both slits? — tom

If an electron is a wave, yes.

You have offered no reason to think that the laws of physics are logically necessary. — Pierre-Normand

So what are we talking about now? I edited my previous post. Note that I mentioned we can discuss Leibniz further in another thread if you like.

So what are we talking about now? — Mongrel

You had issued a challenge for me to show "what properties physical possibilities have that logical possibilities don't or vice versa." I was merely responding to this challenge. It may not be physically possible for you to jump 10 feet high right now, but unless the physical laws that account for you not having this ability can be derived from logical laws, and hence aren't contingent, then it is logically possible that you would do so.

You had issued a challenge for me to show "what properties physical possibilities have that logical possibilities don't or vice versa." I was merely responding to this challenge. It may not be physically possible for you to jump 10 feet high right now, but unless the physical laws that account for you not having this ability can be derived from logical laws, and hence aren't contingent, then it is logically possible that you would do so. — Pierre-Normand

If physical law is necessary, then the set of all physical possibilities is the same as the set of all logical possibilities. Right?

Drop the issue of entailment. It's irrelevant. All that's required for statements of physical law to be necessarily true is that it's true that the universe couldn't have been any other way.

If an electron is a wave, yes. — Mongrel

The electron (and the photon) are particles according to the Standard Model. Anyway, the point is, what will happen is determined by the laws of physics.

As a matter of fact, it can be shown that "physical possibility" is an infinitessimal fraction of "logical possibility", so they are not the same thing.

As a matter of fact, it can be shown that "physical possibility" is an infinitessimal fraction of "logical possibility", so they are not the same thing. — tom

Cool. How is that shown?

If physical law is necessary, then the set of all physical possibilities is the same as the set of all logical possibilities. Right? — Mongrel

No. If physical laws are logically necessary then the set of all physical possibilities is the same as the set of all logical possibilities.

Drop the issue of entailment. It's irrelevant. All that's required for statements of physical law to be necessarily true is that it's true that the universe couldn't have been any other way.

Rather, what is required for statements of physical law to be logically necessarily true is that that the universe couldn't logically have been any other way. You haven't given any indication as to why you think the world could not logically have been different than it actually is.

Your attempt at demonstrating that physical and logical necessity are co-extensive relies on your using "necessarily" equivocally as if there were just one kind of necessity. This is question begging. Of course if you assume that the world can't logically be any other way than the way (actual) physical laws specify it to be, then those two sorts of necessity collapse into one.

You haven't given any indication as to why you think the world could not logically have been different than it actually is. — Pierre-Normand

No. I haven't. What I note is that your argument starts with a hidden premise:

The universe could have been some other way.

You attempt at demonstrating that physical and logical necessity are co-extensive relies on your using "necessarily" equivocally as if there were just one kind of necessity. This is question begging. Of course if you assume that the world can't logically be any other way than (actual) physical laws dictate it to be, then those two sorts of necessity collapse into one. — Pierre-Normand

I asked you for an argument. Why are you saying that I was attempting to demonstrate something?

Your argument has as a premise that the universe could have been some other way. Why should I believe that? What do you know about the natural history of the universe that no physicist currently does?

The universe could have been some other way. — Mongrel

Well sure. Either the universe could or could not logically have been any other way that the way it actually is. Only in the case where it could not logically have been any other way than the way it actually is do the concepts of logical and physical necessity collapse into one. In that case, everything that is actual is logically necessary and nothing that isn't actual is logically possible. This would be the case if and only if the laws of physics, and also the boundary conditions of the universe (the "initial state") were uniquely derivable from the laws of logic (propositional logic? first order predicate logic?). But why would anyone assume this?

Only in the case where it could not logically have been any other way than the way it actually is do the concepts of logical and physical necessity collapse into one. — Pierre-Normand

I don't think so. Suppose some new discovery reveals to us that the universe couldn't have been any other way (no specifics required... all we need is that such a thing is conceivable.) We'll call it the GNSD (great new scientific discovery.)

If it's true that the universe couldn't have been any other way, then laws of physics are necessarily true statements (though we may not have previously known that.)

So while we didn't know it, we said that logical possibility outstrips physical possibility. Post-GNSD, we realize we were always wrong about that. When we imagined gravity causing things to repel one another rather than attract, we didn't realize that this would conflict with a necessarily true statement and therefore, it's not logically possible.

Problem?

What do you know about the natural history of the universe that no physicist currently does? — Mongrel

Physicists investigate empirical laws of physics. They don't know them to be logically necessary. We may suppose, if you like, that, unbeknownst to us, those laws are logically necessary. In that case, the concepts of logical possibility and physical possibility would be co-extensive. But they still are different concepts since, for all we know, the laws of physics possibly are not logically necessary. (Not that "for all we know ... possibly ..." is an epistemic modal notion: yet another concept of possibility that isn't equivalent to logical necessity).

In that case, the concepts of logical possibility and physical possibility would be co-extensive. — Pierre-Normand

Maybe a Hesperus/Phosphorus type of difference. Anyway, for the discerning eye, we just affirmed that the answer to the title of the thread is:

YES.

Maybe a Hesperus/Phosphorus type of difference. — Mongrel

Not quite the same. The necessity of identity is metaphysical, it is neither logical nor physical.

Anyway, for the discerning eye, we just affirmed that the answer to the title of the thread is:

YES.

No, its not a matter of faith since even if one were agnostic regarding the sort of necessity that attaches to physical laws, and even if those laws were deterministic, compatibilists would not be worried about it. Conversely, hard determinists would deem us to be unfree even if the laws of physics were contingent. The impossibility for one not to be constrained by the laws of physics, and/or by the past state of the universe, are irrelevant to the existence of compatibilist free will or to the hard determinist's denial of the existence of free will.

Not quite the same. The necessity of identity is metaphysical, it is neither logical nor physical. — Pierre-Normand

I was talking about intensional vs extensional definition.

No, its not a matter of faith since even if one were agnostic regarding the sort of necessity that attaches to physical laws, and even if those laws were deterministic, compatibilists would not be worried about it. Conversely, hard determinists would deem us to be unfree even if the laws of physics were contingent. The impossibility for one not to be constrained by the laws of physics, and/or by the past state of the universe, are irrelevant to the existence of compatibilist free will or to the hard determinist's denial of the existence of free will. — Pierre-Normand

Good lord. Walked all the way to the top just to fall straight back down.

I was talking about intensional vs extensional difference. — Mongrel

OK, yes, if the laws of physics were logically necessary, unbeknownst to us, then the difference between the two concepts of necessity (physical or logical) would show up merely in intensional contexts of belief attribution.

As Tom as alluded to, though, and as some philosophers of science (e.g. Marc Lange) have argued, many natural laws are contingent if only because they are merely locally valid within specific sub-regions of the world (or 'quantum multiverse'). The concept of a physical law being valid only if it has the form of a true unrestricted universally quantified statement is questionable. This concept doesn't capture the way laws of nature are conceived of in actual scientific practice and it misconstrues the logic of ceteris paribus clauses. It is a concept that sneaks in contentious reductionist assumptions regarding material constitution.

The concept of a physical law being valid only if it has the form of a true unrestricted universally quantified statement is questionable. — Pierre-Normand

Obviously what happens in a black hole stays in a black hole. We were talking about whether the whole universe could have been different.

It is a concept that sneaks in contentious reductionist assumptions regarding material constitution. — Pierre-Normand

Reductionists are always sneaky... like Communists and the Devil.

Obviously what happens in a black hole stays in a black hole. We were talking about whether the whole universe could have been different. — Mongrel

We were also talking about the meaning of "could have been different". I don't know what the point of your comment about black holes is. Some natural laws of insular ecology apply only to island ecosystems and some natural laws of chemistry apply only to aqueous solutions in thermodynamic equilibrium. That's the sort of locality I was referring to. The relatively broader range of applicability of the "fundamental" (so called) laws of physics proper just is a matter of degree, and also a matter of their abstracting away most (thought not all) the substantial-formal features of the material objects talked about. This is what makes them look like (unrestricted) universally quantified statements rather than like attributions of constitutive (albeit fallible) natural powers to contingently existing natural substances.

Some natural laws of insular ecology apply only to island ecosystems and some natural laws of chemistry apply only to aqueous solutions in thermodynamic equilibrium. — Pierre-Normand

The concept of natural law isn't without its critics. Having to point out when and where a rule applies isn't much of a threat, is it?

The concept of natural law isn't without its critics. Having to point out when and where a rule applies isn't much of a threat, is it? — Mongrel

It means that whether or not such a law applies here and now depends on the surrounding conditions here and now. The applicability of this law (and hence the validity of its status as a law) depends contingently on the local conditions. The apparatus of modal logic thus applies where "possible worlds" range over the attainable variations in local conditions. A "compatibilist" about free will can define possibilities for action as possibilities within such a range of contingent conditions. Human agents have both the power to do A, and to abstain to do A, just in those cases where the actual conditions determining whether or not they do A were set by the agent herself, and can thus be traced to her reasons for acting.

It may nevertheless appear that, in case where the actual conditions of the agent are C, and it is a law that the agent does A in conditions C, that the agent didn't have the power to abstain from doing A. But this is a mistake since it is no accident why the agent found herself in conditions C, such that she would "necessarily" (i.e. from physical necessity) do A in the actual circumstances; it is precisely because she had a reason to do A in those circumstances that her conditions were set to C (as a result of the normal functioning of her cognitive abilities and of her underlying physiology). If she had had reasons to abstain from doing A, counterfactually, then her conditions would also have been different and it is her power to abstain from doing A that would rather have been actualized.

It looks to me like you've built an edifice of complete absurdity.

It looks to me like you've built an edifice of complete absurdity. — Mongrel

What is absurd? You seem to equate actuality with necessity, and I can understand that from such a point of view the very idea of unactualized powers (in general, or unactualized powers of human agency in particular) can seem absurd. Likewise, from the point of view of radical skepticism, perceptual knowledge of the external world may seem absurd. But from a common sense perspective the notions that I am defending against philosophical prejudice are truisms rather than absurdities. It is rather the dogmatic assimilation of actuality and necessity, without argument, that is absurd.