Once more: is there such a thing as metaphysical necessity?

Some philosophers distinguish among three classes of necessary (or, conversely, impossible) things: (i) physical necessities (and impossibilities), meaning things that are going to happen (or can never happen) because of the ways the laws of physics are; (ii) logical necessities (and impossibilities), that is things that are true (or impossible) because of the laws of logic; and (iii) metaphysical necessities (and impossibilities), meaning things that are the case (or can never be the case) because of…? Yeah, the latter is the problematic one. Nobody doubts the existence of the laws of physics (though some philosophers reject that kind of talk and prefer to think in terms of causal regularities). Some people think that logical necessity / impossibility is actually the result of human constructs, since one can adopt different kinds of logic, but this is controversial. And then there is a small number of philosophers, the metaphysicians (sometimes they call themselves metaphysicists) who insist on a separate existence of the third category. And this is very controversial.

I wrote about metaphysical necessity / impossibility back in 2014, and then again (on the specific issue of “grounding”) in 2015. In both cases, I was rather skeptical of distinguishing metaphysical anything from either the physical or the logical realm. The way I saw it was this: logical necessity / impossibility > physical necessity / impossibility > contingency. That is, if something is, say, logically impossible, it is a fortiori physically impossible, and it can’t happen no matter what the specific circumstances. However, if something is happening, then it must be both physically and logically possible. And so forth. My argument in the past is that whatever examples of alleged metaphysical necessity / impossibility one would come up with it would either turn out to belong to the physical class or to the logical one, with nothing either in between or, somehow, above logic.

(For the rest of this discussion I will bracket two obvious questions: (a) where do the laws of physics come from? And (b) if logic is a human construct, then in what sense can we talk about logical necessity / impossibility? The only hint that I will give here is that I think the laws of physics themselves are a human construct, but they reflect a fundamental structure of reality. Something similar may be going on with logic. So there…)

Recently, a friend of mine and former student at CUNY’s Graduate Center (she has just successfully defended her thesis!) Antonella Mallozzi, has put out a very conveniently and nicely put together diagram to explore (and defend, in her case) the idea of metaphysical necessity as distinct from both the physical and the logical varieties. With permission from Antonella, I reproduce the diagram below, as it will guide us through the rest of the discussion. (Antonella has also guest edited a special issue on this topic for the journal Synthese, entitled “New directions in the epistemology of modality.” You can see her leading article here. I hear that my colleague Graham Priest, one of the best logicians out there, is also skeptical of the notion of metaphysical necessity, but I have purposely not read his paper, currently in print, so to be able to develop my own ideas.)

So what I’d like to do now is to go through each of Antonella’s possibilities for metaphysical necessity, briefly look at the examples that she presents, and see what happens. We will start with the right-center portion of her large circle (labelled “general metaphysical necessities”) and proceed counter-clockwise, one category and set of examples at a time.

(I) Logical, mathematical, and geometrical necessity (middle right of the large circle). Her examples here include “necessarily, everything is self-identical,” and: “necessarily, two plus two equals four.” As she points out, some philosophers are skeptical that these are examples of necessity, or that these statements are true, pointing to the existence of non-classical logics, non-euclidean geometries, etc. But I’m going to accept these examples as valid given certain axioms (classical logic, euclidean geometry, and so forth). You may disagree, of course, but as I mentioned above, I’m going to bracket any further discussion of this particular issue. Even if we do accept the examples, however, they fall squarely into the logical end of my continuum above, they are not distinctly metaphysical.

(II) Conceptual necessity (upper right of the large circle). Antonella here distinguishes between things that are epistemically necessary, but not metaphysically so (the part of the small conceptual circle that lies outside the largest one), and things that are both epistemically and metaphysically necessary (the little bit of the small conceptual circle that lies inside the largest one). An example of alleged epistemic (but not metaphysical) necessity is the following: “Julius” designates the inventor of the zip. It then is a priori (epistemically) necessary that if anyone invented the zip, Julius did. This seems to me a very weak sense of epistemically necessary, since it simply states that given that X is true, you better take X to be true. I think the use of the word “a priori” is misleading here, as it is obviously a contingent fact that Julius, and not someone else, invented the zip. More importantly, because of the latter possibility, even Antonella agrees that this is a case of metaphysical contingency.

What about metaphysical conceptual necessities? Antonella gives two examples: “necessarily, anything colored is extensive,” and “necessarily, there is a valley in between two mountains.” She also adds, however, that some people think these are logical, not distinctly metaphysical necessities. The case seems particularly clear for the second example: once one defines mountains as things that have peaks and are surrounded by valleys, then it is obviously logically necessary that if there are two mountains next to each other they will be separated by a valley. As far as the color example is concerned, it sounds to me like a case of contingency due to biology: colors are not “out there,” but rather the result of the interaction between physico-chemical properties of materials and the specific physiological and perceptual apparatus of a given organism. Perhaps one could say that more obviously intrinsic physical properties necessitate extension (meaning, something more than a geometrical point), but now that begins to look like a physical necessity, and even that is doubtful, if one accepts certain radical views of what actually constitutes the physical world.

(III) Grounding and mereology (top of the large circle). Antonella’s examples are “necessarily [P&Q] is grounded in [P], [Q],” and “necessarily, everything is a part of itself.” I have expressed my skepticism about the concept of grounding in metaphysics elsewhere (it’s pretty vague and slippery, and doesn’t seem to add anything), but Antonella herself comments that some people would consider these examples of logical necessity, not a distinctive metaphysical class.

(IV) Ethical-deontological necessities (upper left of the large circle). “Necessarily, violence is wrong.” Well, no. My ethics is a naturalistic one, so I don’t think there is anything that is necessary in that realm, at all. Ethics is very clearly, to me, a human construction, constrained by our biology as social animals capable of language, which means it isn’t entirely arbitrary, but also that there is nothing necessary about it. I am, most definitely, not a deontologist.

The last two classes of metaphysical necessities proposed by Antonella are important, because they fall into the circle labelled “distinctively metaphysical” (or Kripkean, in honor of the highly influential philosopher Saul Kripke, currently at CUNY’s Graduate Center). That is, in her mind these are the ones that cannot be reduced in any way to logical or physical necessities, so let’s pay particular attention.

(V) Causally-nomic (lower left of the large circle). Even Antonella readily admits that it is controversial whether anything at all falls into this group! Her examples include the laws of physics and chemistry, but it is an open question to say the least why the fundamental laws of physics are the way they are (those of chemistry, presumably, can be reduced to physics). It may be that they could not possibly have been different, because of the way the causal world is structured; or perhaps they could have been different, and the ones we observe are that way because of contingency. The first scenario would seem to be a case of physical necessity, while in the second scenario the only constraints would be imposed by logical impossibility and necessity. Again, no distinctive metaphysical criterion appears to be required.

(VI) Finally, we get to the most promising class, that of “de re,” a posteriori things that have their source in the fundamental nature, or essence, of things (lower part of the large circle). The pertinent examples are classics of the metaphysical literature: “necessarily, water is H2O,” or “necessarily, I could not have had different parents then the ones I actually have.” I am, however, utterly unconvinced. Water is H2O either as a matter of physical necessity (if the laws of physics could not have been otherwise) or it is a contingent fact about our universe (if the laws of physics could have been different). As for my parents, that seems an entirely contingent fact of our biology. For instance, if humans were a clonal species that reproduced by budding, “I” could have had a lot of different specific parents and still be “me” (not to mention that this example depends on one’s conception of personal identity, a controversial issue in its own right).

I guess this third look at metaphysical necessity / impossibility, despite Antonella’s brave and very clever attempt, still leaves me unmoved. I keep thinking that the logic > physics > contingency conceptual scheme is sufficient to account for all examples that have been presented, and that metaphysics is an artificial category situated between logic and physics: each alleged example of metaphysical necessity turns out, upon closer inspection, to be either a case of logical necessity, or one of physical necessity. But I remain open to be convinced otherwise. Stay tuned for a fourth possible look at the issue, a few years down the road!

107 thoughts on “Once more: is there such a thing as metaphysical necessity?

  1. Hugh Jidiette

    Massimo,

    But if metaphysical possibility reduces to physical possibily why do we need it?

    Because it’s a substantive and controversial claim to say that. It’s a substantive metaphysical claim to say that the ways the world really could have been just is the physically possible ways. By contrast, it’s not a substantive claim to say that the physically possible ways just is the physically possible ways.

    Suppose that, according to the laws of nature of the actual world, nothing can travel faster than light. Given that, I think that the world couldn’t have turned out such that things could travel faster than light. This will be controversial claim. The notion of metaphysical possibility is needed for me to make this claim.

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  2. Disagreeable Me (@Disagreeable_I)

    Hi Bunsen

    I am not certain what it can mean for something to be physically necessary without a mathematical theory underlying the phenomenon.

    That’s only because physical necessity is strictly weaker than mathematical necessity. Physical necessity is about what must be the case given the particular mathematical laws of physics of our particular world. Mathematical necessity is broader in scope, being about what must be the case in arbitrary mathematical systems.

    Finitists exist, as do Ultafinitists.

    Interpret Robin to mean there is no possible world where Euclid’s theorem doesn’t work, given the axioms Euclid adopted. That’s a separate issue to finitism or ultrafinitism.

    Hi Massimo,

    Forgive me the pragmatic quip, but then why bother?

    Because I find the claims of those who advocate for the concept of metaphysical necessity to be intelligible. I know what they mean, even if I personally believe that it maps precisely onto mathematical or logical necessity. Similarly, I don’t personally believe in God, but I find the concept of God to be (somewhat) intelligible and I wouldn’t dismiss it a priori as redundant.

    A 1D world is logical possible but physically impossible.

    That’s a category mistake, in my view, in that it doesn’t make sense to discuss the physical impossibility of possible worlds other than our own. Physical impossibility is only applicable to things in our world. You wouldn’t say that it is physically impossible for there to be a possible world where the fine structure constant is different than it is in ours, would you? You can only say that the physics of that world is different from the physics of ours. Similarly, the possibility of worlds with very different laws of physics from ours (such as having 1D space) is a metaphysical issue. If you think all such worlds are genuinely possible ways the world could have been, then you think metaphysical possibility maps onto logical possibility as I do. Otherwise you think there is a difference between metaphysical and logical possibility.

    Hi Robin,

    rather it was a claim about the scope of that logical necessity, in particular it was a claim about an absolute constraint upon the kinds of realities that are possible. If that is not a metaphysical claim then I don’t know what is.

    It’s a metaphysical claim certainly. And I am making metaphysical claims too. But if that claim is just that only logical or mathematical contradictions rule out the possibility of a world, then that metaphysical claim is that metaphysical possibility/necessity reduces to logical/mathematical possibility/necessity.

    Hi Dan,

    just strike me as quick and glib and completely underestimate the seriousness and intelligence of those advancing the relevant positions

    Perhaps, but perhaps you are also underestimating the seriousness and intelligence of those arguing against the relevant positions. I don’t think anyone here is trying to dismiss these ideas glibly, I think they are summarising the conclusions they have come to after consideration.

    Putnam and Kripke are brilliant, certainly. Their ideas deserve careful consideration and thought, certainly. And I have thought about them quite a bit, and unfortunately I find that I disagree. If you’re telling me it is inappropriate for me to disagree with professional philosophers then I’m afraid I will have to break that rule once again and disagree with you!

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  3. Disagreeable Me (@Disagreeable_I)

    Hi Massimo,

    Missed this one:

    Except that isotopes have different characteristics, thus violating Antonella’s assumption about essences.

    No violation here. Antonella doesn’t say that all characteristics of something with an essence have to be immutable for something to have an essence. Antonella is saying that the essence of something is those particular characteristics of it that cannot change without it turning into something else. The essence of silver is to have 47 protons in the nucleus. As long as that doesn’t change, it’s still silver. If it does change, then it isn’t silver any more. This, of course, is correct, as far as it goes. The fact that there are different isotopes of silver is not at all a counter-argument to Antonella’s claim.

    But I think you’re on the right track when you say that these kinds of hard rules are the exception rather than the rule, and that essences might be harder to justify in biology for example.

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  4. Disagreeable Me (@Disagreeable_I)

    Hi again Massimo,

    To quote myself:

    Antonella doesn’t say that all characteristics of something with an essence have to be immutable for something to have an essence.

    On reflection, I can see where you’re coming from, in that she does say that all the properties of silver arise due to its essence of having 47 protons in the nucleus, including boiling point, melting point etc, and you are certainly right that different isotopes have different boiling and melting points. I think Antonella would say that the atomic number constrains rather tightly the isotopes that are possible, and then the boiling and melting points of the different isotopes are therefore explained somewhat indirectly by the atomic number because those isotopes themselves are accounted for with reference to the atomic number.

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  5. Markk

    Massimo,

    You said:

    “The laws of physics are not anywhere in particular, they are a shorthand for us to describe the regularities of the universe.”

    But just now:

    “To me causal links between phenomena are of a certain kind because the laws of physics are what they are.”

    Which just seems problematic to me. If the answer to “why are there causal regularities” is the laws of physics, and the laws of physics are just descriptions of causal regularities, then talk of “laws of physics” adds nothing whatsoever and they should be replaced by something that does do the explanatory work required. Unless I’ve missed something.

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  6. Robin Herbert

    Brodix

    No highest prime would go to infinity as a metaphysical necessity, though, as Bunsen observes, there is resistance to it.

    There are also flat earthers and creationists.

    There is no highest prime as a matter of logical necessity. The fact that someone could arbitrarily attach the label ‘prime number’ to some object does not alter this.

    I could decide one day that ‘prime number’ means ‘the number 42’ and then it would be true that there was only one prime number.

    But it would be silly to say on this basis that there is doubt about there being more than one prime.

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  7. Robin Herbert

    Massimo

    Right, that’s what I mean when I talk about possible worlds. If any world implies a logical or mathematical contradiction/incoherence then it cannot exist.

    That in itself is a statement about the kind of world’s that can and cannot exist and therefore a metaphysical claim.

    There is no logical necessity that logic must be the same in every possible world unless you include that as an axiom.

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  8. Markk

    Alan above mentioned an “inherent characteristic in nature”.

    Which I think is much more promising than talk of “laws of physics”.

    Laws of physics originally were a replacement for final causation. Final causation did posit an inherent characteristic in nature, while the introduction of laws of physics relocated this in something external ie. God as Lawgiver.

    The removal of God from the picture thus requires, in my view, a replacement for laws of physics. But even if you do believe in God (as I do), the advantage of explaining causal regularities by reference to internal characteristics rather than something outside just seems more sensible.

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  9. Alan White

    Massimo–

    “To me causal links between phenomena are of a certain kind because the laws of physics are what they are. If they were different, the causal links would be different as well.”

    I agree. That is why my one-to-one event relationship would be causal not just in this world, but even in one far enough from this one as to have different laws but adhering to the description in those cases. Both thus metaphysically causal but different in terms of physical necessity (as a world-bound concept relative to laws that obtain in the world).

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  10. Robin Herbert

    From the Wikipedia article on Ultrafinitism:

    Like other strict finitists, ultrafinitists deny the existence of the infinite set N of natural numbers, on the grounds that it can never be completed.

    I can see their mistake right there. N doesn’t exist in any other sense that it is an abstract definition that can be the object of a quantifier, neither do any of the sets they define.

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  11. Robin Herbert

    Irrelevant in any case since both finitists and ultrafinitists agree that there is no highest prime number, so they are not such absurdists as I was initially led to believe.

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  12. Robin Herbert

    DM

    It’s a metaphysical claim certainly. And I am making metaphysical claims too. But if that claim is just that only logical or mathematical contradictions rule out the possibility of a world, then that metaphysical claim is that metaphysical possibility/necessity reduces to logical/mathematical possibility/necessity.

    Not unless you can construct a logical argument demonstrating this without including the axiom that logic holds the same in all possible worlds.

    There is no logical necessity that logic holds the same in every possible version of reality.

    So the claim that there is no possible version of reality where there is a highest prime number cannot be considered a claim of logical necessity.

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  13. Robin Herbert

    And what does “physical necessity” mean? Does it mean “necessitated by the way physics is”, or “necessitated by all the ways physics could be or could have been”?

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  14. Robin Herbert

    Massimo

    biologists have moved away from Aristotelian essentialism ever since Darwin, and for good reason. There is no essence shared by all fish or mammals, only a phylogenetic relation and a statistical, dynamic cluster of properties.

    I am almost sure I have read Aristotle also saying that there is no essence shared by fish and that the classification method he was proposing was hard to define and imperfect (“History of Animals”). I didn’t think Aristotlean essentialism worked that way.

    But it does seem to have been a useful distinction between the superficial similarities between bones and spines and the ‘essential’ similarities between bones of different mammals.

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  15. brodix

    The concept of law is reductionist and static, while the processes creating these effects are holistically dynamic.

    In the void there would be no laws, not even geometry, because form, definition, distinctions, etc need to be expressed to exist and to be expressed, they need to be active. Form without motion would still equate to a temperature of absolute zero. The vacuum has to fluctuate, for anything to exist.

    So to have laws you need process. Yet the function of minds is to distinguish forms, while it is the function of the gut to process the energy manifesting the mind.

    We were a gut, long before we were a mind, yet our minds break everything down to bits and assume “it” is emergent from the bits. Overcoming this mental bias requires stepping outside the box of forms, even if only to look back at them. We think of the brain as a bunch of neurons, registering information, but it is the flow of blood powering it. Energy is the medium, form is the message.

    Energy goes past to future. Information goes future to past. Tomorrow becomes yesterday because the earth turns and the sun shines.

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  16. SocraticGadfly

    Nice name, Hugh. Are you also the same handle on Twitter, where I checked before clicking your link to see if it led to a blog? (A name like that sounds exactly like a Twitter handle.)

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  17. Disagreeable Me (@Disagreeable_I)

    Hi Robin,

    Not unless you can construct a logical argument demonstrating this without including the axiom that logic holds the same in all possible worlds.

    Massimo explicitly bracketed off this line of argument. The position that logic might work differently in different worlds is a view held by some, but it is not a widely held view and we are assuming for the sake of this discussion that this view is false.

    But in any case you seem to be saying that logic might work differently in different worlds, and yet that it is a metaphysical law that logic works the same in all worlds (no possible world where there is a greatest prime). Having your cake and eating it too? If it is not logically necessary that there is no world where there is a greatest prime, I don’t know how you would justify the claim that there is no possible world where there is a greatest prime.

    I guess you could construe this as a metaphysical law if you like, but I would say that it is a category error (and so a logical error) to even raise the question of how logic works in a particular world — logic is not part of a world but is its own thing. I’m not going to argue this point further because Massimo indicated it was out of scope.

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  18. Robin Herbert

    The point is that even if we disagree with Graham Priest when he says “Every state of affairs is logically possible” we still cannot appeal to logic to demonstrate that the same logic applies in every possible world. So there is no logical impossibility in their being a world in which there is a largest prime number.

    And it has nothing to do with physical impossibility because the claim that there is a possible world in which there is a largest prime number does not presuppose that our physics holds in that world.

    So if it is true that there is no possible world in which there is a largest prime number then it is neither a logical nor a physical necessity, but it is still a necessity.

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  19. Philosopher Eric

    I like to think of metaphysics essentially as a founding platform from which to begin. For example I consider Rene Descartes’ “I think therefore I am” to be a profound bit of metaphysics. As I see it both the theist who claims that Jesus is their savior, and the physicalist who claims that all of reality functions causally, are making metaphysical claims. Einstein was preaching naturalistic metaphysics when he asserted “God does not play dice”, just as physicists who dispute this display supernatural metaphysics with their non-causal interpretation of Heisenberg’s Uncertainty Principle. My single principle of metaphysics is a platform from which to potentially build as well. With it I hope to help marginalize those in academia who pedal “faith” over “reason”. (If vindicated I suspect that the great stain on Einstein’s career will find it’s way to his opponents.)

    Metaphysical necessity/ impossibility suggests an independent method from which to look at things, not a foundational position from which to potentially build. Of course the term needn’t be defined as I define it, though I do consider this particular iteration useful. We found our beliefs about reality upon both implicit and explicit positions. Does anyone have a better term for the beginnings to this process, than “metaphysics”?

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  20. davidlduffy

    Alan’s comments about causation along with Hugh’s on the superluminal reminded me that physicists are very happy to talk about causation, and are generating a sizeable literature on the consequences of closed time-like curves eg

    https://www.nature.com/articles/ncomms5145

    “[Under the Deutsch 1991 model] quantum mechanics therefore allows for causality violation without paradoxes, while remaining consistent with relativity…[but allowing] the solution of NP-complete problems in polynomial time, unambiguous discrimination of any set of non-orthogonal states, perfect universal quantum state cloning and the violation of Heisenberg’s uncertainty principle”

    So is time travel physically impossible, logically impossible or metaphysically impossible?

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  21. Bunsen Burner

    No, physicists talk about causality. This is about the time ordering of events in spacetime. It’s probably a necessity for talking about causation, however as quantum mechanics shows, you can have causality without causation.

    As for the possibility of time travel, I would rule it out on logical grounds, but since Dialetheists exists, I guess we will have to wait for what future quantum theory of gravity has to say on the matter.

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  22. Bunsen Burner

    There is no such thing as a world where there may or may not be a largest prime. Statements about primes exist in a model of a particular formal system constructed by minds. If your world doesn’t have any minds, or minds that don’t care about your formal system then it’s meaningless to talk of primes in that world. In fact, in our world, first order Peano arithmetic has an infinite number of non isomorphic models. Which of these models and their statements about primes are to be considered metaphysical?

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  23. Massimo Post author

    Socratic,

    is it not possible that a different “Big Bang,” etc., in producing a different universe, different substances, different physical laws, etc., would have produced ones in which what constitutes logical incoherence is different than in our world?

    That very much depends on how you think of logic. If you think it picks up something “out there” then the answer is no. If you don’t, then the answer is no. It may appear that there is a tension with Platonism here, because how could logic pick something out there if it is a human construct? But scientific theories are also human constructs, and yet…

    Hugh,

    It’s a substantive metaphysical claim to say that the ways the world really could have been just is the physically possible ways. By contrast, it’s not a substantive claim to say that the physically possible ways just is the physically possible ways.

    Take “metaphysical” out of those phrases and you lose nothing. Yes, they are substantive or not that substantive claims, based on logic and physics.

    DM,

    Because I find the claims of those who advocate for the concept of metaphysical necessity to be intelligible.

    Oh, I find them intellegibile too. Just superfluous, because they don’t do any work beyond physics and logic. Just like God.

    Antonella doesn’t say that all characteristics of something with an essence have to be immutable for something to have an essence. Antonella is saying that the essence of something is those particular characteristics of it that cannot change without it turning into something else.

    But that’s convenient, unless there is a principled way to make that distinction. According to your version, she gets to arbitrarily define essences as she likes, then turn around and claim that her concept of essence is empirically based.

    Antonella would say that the atomic number constrains rather tightly the isotopes that are possible, and then the boiling and melting points of the different isotopes are therefore explained somewhat indirectly by the atomic number.

    Which strikes me as basic physics, nothing to do with metaphysics. Also don’t forget that that sort of example of essences — problematic as it already is — is almost impossible to extend to anything else, like more comoplex physical objects, not to mention biological ones.

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  24. Massimo Post author

    Markk,

    If the answer to “why are there causal regularities” is the laws of physics, and the laws of physics are just descriptions of causal regularities, then talk of “laws of physics” adds nothing whatsoever and they should be replaced by something that does do the explanatory work required

    Unless one has an account of why those regularities are the way they are, which is the current objective in fundamental physics. Besides, do you think that adding “metaphysical” to the whole thing adds something?

    Robin,

    There is no logical necessity that logic must be the same in every possible world unless you include that as an axiom

    How would you know? You either have to deny that axiomatically or introduce some kind of meta-logic that would establish it. In either case, bringing in metaphysics doesn’t seem to help.

    Also, careful here, because metaphysicians themselves have to invoke logic, at least losely speaking, in order to talk about “possible” worlds at all. Otherwise what differentiates a possible from an impossible world? Remember that Antonella explicitly said that she wants to avoid the Chalmers route, talking about possibilities in terms of conceivability.

    Alan,

    That is why my one-to-one event relationship would be causal not just in this world, but even in one far enough from this one as to have different laws but adhering to the description in those cases. Both thus metaphysically causal but different in terms of physical necessity (as a world-bound concept relative to laws that obtain in the world).

    I think I get your point, but causal interactions are the result of the way a particular world is. If we change the rules for the world, so to speak, then we get different causal interactions. Some causal interactions may hold across some worlds, but that would still be a result of how the rules are set up, and therefore still under the purview of physics.

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  25. Massimo Post author

    Robin,

    what does “physical necessity” mean? Does it mean “necessitated by the way physics is”, or “necessitated by all the ways physics could be or could have been”?

    The former, in this universe. When we are talking about the latter, then we are talking about possibilities constrained by logic.

    The point is that even if we disagree with Graham Priest when he says “Every state of affairs is logically possible” we still cannot appeal to logic to demonstrate that the same logic applies in every possible world.

    I do disagree with Graham here. What does he mean by a state of affairs? Is it possible in a different world to square the circle? I don’t think so. You may be right about not being able to appeal to logic for that, but if not then we are left with nothing. There is no other principled way of doing it that I can see.

    David,

    So is time travel physically impossible, logically impossible or metaphysically impossible?

    There is a large literature on that, and the answer may turn out to be either (not both: if it is logically impossible, then a fortiori it is physically impossible). But, again, I see no principled way in which one could instead propose a metaphysical answer to the question.

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  26. Bunsen Burner

    No one has mentioned one often discussed necessity – the theological idea of a necessary being. Assuming anyone finds this coherent, would that be an example of a metaphysical necessity?

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  27. Philosopher Eric

    David,
    I’m not too sure about the passage that you’ve quoted but I would like to give your question a try.

    So is time travel physically impossible, logically impossible or metaphysically impossible?’

    . My thought is that it isn’t ultimately known that time travel is impossible, though saying that it’s logically impossible would at least be a category error. As I’ve just submitted, metaphysics can usefully be defined as a founding position from which to begin, rather than some kind of independent method from which to look at things, as seems popular in philosophy. A theistic metaphysical founding versus a causal metaphysical founding would clearly be at odds. But if we go the causal route, which would be fitting since it’s the only one in which things have the potential to be figured out (per my single principle of metaphysics), modern evidence does suggest that “c” is an ultimate limit.

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  28. Daniel Kaufman

    A term is rigid if it denotes the same object in all possible worlds. Kripke argues that proper names are rigid in this way. In a possible world in which Nixon didn’t resign the presidency, “Nixon” would still refer to Nixon. This is Kripke’s argument against the description theory of names, according to which the meaning of the name “Nixon” is a cluster of descriptions that uniquely pick out the man in the actual world: i.e. “the President who orchestrated the Watergate break-in and later resigned the presidency.”

    Kripke argues that natural kind terms also denote rigidly, something that is also implied by Putnam’s work, especially “The Meaning of ‘Meaning’.” The idea is that the word ‘water’ denotes the same substance in every possible world, rather than referring descriptively. Otherwise, one would have to say that in a possible world in which an alien compound — XYZ — had all the descriptive properties of H20 in the actual world that XYZ is water, which both Kripke and Putnam argue has to be mistaken.

    If natural kind terms refer rigidly, then that means they refer to the same thing in all possible worlds. Thus, the natural kind in question is necessarily such-and-such. And it is this that leads Kripke and others to metaphysical necessity.

    Some in this discussion have said that metaphysical necessity is just logical necessity, but Kripke has rejected this and again, one has to engage with his arguments and not just say so.

    DM: I never said that one cannot disagree with Kripke, Putnam, etc., so I have no idea why you are responding as if I had. What I did say is that one cannot simply dismiss them … or at least, not if one wants to be taken seriously by serious people. As for being glib, I was responding to a particular comment in which metaphysical necessity a la Kripke had been dismissed in a single sentence. If that isn’t glib, I don’t know what is.

    As for your disagreement with Kripke and Putnam’s arguments, that’s all fine and well. I’m not very confident however that you understood them. I certainly wouldn’t have, until I’d received quite a bit of higher level philosophy education; education that you have not had. It isn’t stuff you can just pick up and read and get.

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  29. SocraticGadfly

    Massimo, my take on logic is that it is, no more than mathematics, something “out there.” Therefore, yes, I think it is possible that logical coherence would be different in some other possible worlds than our actual one.

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