Friday, March 20, 2009

Like Matteo, I've been thinking about haecceitism. I claim it is best pronounced the way Kaplan liked it: Hex'-ee-i-tis-m. I'm not sure why I care about this, but I do.

There is a lot of older stuff in the metaphysics literature (Black, Adams, etc.) and a lot of more recent work in the philosophy of physics literature (Saunders, Ladyman, French and Krause, etc.) and the two discussions don't have a lot of points of contact. (Disclaimer: I'm going to read Katherine Hawley's paper on the PII in the next week or so; perhaps this will join the two debates together a bit more for me.)

Here are a few things I find confusing. (1) The physics people often seem to run together (sometimes on purpose) epistemological issues about indiscernibility with metaphysical ones. The fact that two particles are indistinguishable for us seems to entail, to some, that they are indistinguishable simpliciter. I'm not clear on what, if any, metaphysical lessons can be learned when we take this sort of strong empiricist stance. (2) Haecceitism is often not well enough defined. Sometimes it means that objects have primitive thisnesses (following Adams) but sometimes it just means objects are (or could be) primitively different. This is an important distinction. The more minimal kind of haecceitism, which I'd argue doesn't even deserve the name, just says we can have objects that are perfect duplicates but nevertheless differ. They don't differ because they have special thisnesses, because they don't have thisnesses. They just differ even without differing in their (non-identity-based) properties. (3) Saunders and others want to sidestep the PII by denying that bosons are objects. They are some other sort of entity. But how does this supposed to help with anything metaphysically interesting? I always took the PII to apply to things of any sort.  

Finally, a note: physicists often make claims about particles being identical when they really mean they are of the same kind.  Argh!


  1. Hi Laurie,

    I have a terminological point. I claim that two things that differ without differing in their non-identity-based properties might nevertheless have different primitive thisnesses in Adams's sense of 'primitive thisness'. That's because, in Adams's terminology, a thisness is just an identity property: the property of being identical to Laurie, for example. (By 'primitive', he just means that it is not equivalent to any qualitative property. An unfortunate use of 'primitive' in my opinion.)

    So if the "minimal" haecceitism that you're describing is consistent with distinct qualitative indiscernibles that differ in their identity-based properties, then you can be a "minimal" haecceitist in this sense and still accept that distinct qualitative indiscernibles can be distinguished by their primitive thisnesses in Adams's sense. So that is just a long-winded way of saying that I think you don't want to use Adams's terminology in explaining the "genuine" sort of haecceitism you were trying to characterize.

    So my question for you is: what did you have in mind by 'primitive thisness' if not Adams's notion of an identity property that is not equivalent to any qualitative property?

  2. "(1) The physics people often seem to run together (sometimes on purpose) epistemological issues about indiscernibility with metaphysical ones. The fact that two particles are indistinguishable for us seems to entail, to some, that they are indistinguishable simpliciter."

    I don't think that's quite right. The issue has to do with statistics and the size of the configuration space. Suppose particles A and B can't be distinguished by us -- maybe because their particle-labels are too small to see even with a very good microscope. But suppose they're different individuals. And suppose the universe has two locations in it. Then the state (A, B) is different from (B, A), and when we're counting up potential physical states we need to have both of them. On the other hand, if A and B are indistinguishable then there's just one physical state. It's the latter consideration that motivates the physicists -- there are cases where you need to "count up the potential states of the universe" and to get the right answers you need to treat (A, B) as the same state as (B, A).

    "Finally, a note: physicists often make claims about particles being identical when they really mean they are of the same kind. Argh!"

    I don't think that's right. Put two electrons in a box, shake it up, and take one out. There is no fact of the matter about which one came out.

    Not to editorialize too much, but my own view is that metaphysicians often pretend that the universe is Newtonian. It doesn't take too much work to learn the physics, especially now that there are readable QFT textbooks available.

  3. chadc:

    I take Adams to mean something rather substantive by "thisness." That is, the identity property is a property in its own right. The minimal view would hold that identity properties supervene on some primitive difference that is not a property.


    In the cases I am interested in, the facts about permutation symmetries are accepted, and the question is what they imply about the PII. It is controversial to "assume they are different individuals."

  4. chadc here--I just figured out how to make my real name show up.

    Adams argues ("Actualism and Thisness") for the thesis that there are no unexamplified thisnesses and that thisnesses depend on their bearers. And, if that is right, it seems natural to suppose that the distinctions among individuals are explanatorily prior to distinctions among the thisnesses which ontologically depend on them. That's roughly the minimal view, right?

    He discusses and rejects the view that what he calls 'haecceities' play the role that he accords to thisnesses. They're kind of neat and exotic: your haecceity h = the property of having h as a haecceity. These haecceities seem to me more like what you mean by 'substantive'--they don't depend for their existence and distinctness from other haecceities on facts about their bearers.

  5. "In the cases I am interested in, the facts about permutation symmetries are accepted, and the question is what they imply about the PII. It is controversial to "assume they are different individuals.""

    1. Contrary to what you wrote in the initial post, the argument the physicists make does not run through epistemology. It's a standard scientific argument. You have an equation that depends on the number of physical states in the universe. If you treat (A, B) as different from (B, A) you get the wrong answer; if you treat them as the same, you get the right answer.
    You then want to explain this fact because you're a scientist. The best explanation anyone's come up with is that the particles don't have individuality. There's no *assuming* going on -- there's an inference to the best explanation, based on an actual empirical result; just like in the rest of science.

    2. There are classical analogues to the phenomenon: imagine you're at a beach, and you watch two qualitatively identical individual waves, A and B, come rolling in. Is there an possible world where wave B preceded wave A? No because, the waves are nothing beyond the motions of the particles in the sea.
    In QFT, you have very similar equations governing individual particles. Based on our knowledge of the classical analogues, you wouldn't *expect* particles to behave as if they had classical individuality, and they don't.

    2. Furthermore, the

  6. Oops, sorry about the trailing nonsense.

  7. hi Chad,

    The distinction I want to make is between a view of duplicates being distinguished by having distinct primitive thisnesses that in some sense capture what each individual *is* (i.e. my thisness is my Laurie-ness), and a mere brute primitive difference between duplicates. The view about primitive thisnesses can serve as a foundation for arguments about transworld identity (which would be harder to make using the minimal difference position). And the strong view is what I take Adams to be defending in, say "Primitive Thisness and Primitive Identity."

  8. Is the Laurie-ness of the strong view the same as the property of being identical to Laurie? If not, then it is certainly not Adams's view, even in PT&PI, since he consistently understands thisnesses as identity properties of individuals. On the other hand, if the Laurie-ness of the strong view *is* the property of being identical to Laurie, then it seems very plausible that Laurie-ness depends ontologically on the existence of you. (I think that view is widespread, anyway, and there are good arguments for it.) And, in that case, it is hard to see how it could explain the distinctness of you and a qualitative duplicate, since you and your duplicate will be ontologically prior to your thisnesses.

    I think that what you should say is that the strong view is the view that there are non-qualitative thisnesses which are not ontologically dependent upon their bearers (and so, plausibly, are not identity properties, since identity properties plausibly are dependent upon their bearers). Then you can say that only the strong view allows us to appeal to thisnesses as *explaining* distinctions among qualitative duplicates. On the weak view, by contrast, the distinctions are just brute facts. If you put things this way, as I think you should, then Adams isn't a proponent of the strong view because his thisnesses are identity properties.

    If I'm right in guessing that you'll agree that Laurie-ness (of the strong view) is not an identity property, then what else can you say about it? Is it coarse grained, for example? On what grounds can we judge it to be non-qualitative?

  9. Hi Laurie,

    It does look like we are currently thinking about (at least partly) the same things, so let me try to say something re. your points.

    1) As I see it, the lesson is supposed to be that physics can provide non-purely-thought-experimental (alleged) counterexamples to PII and, consequently, it constitutes a good ‘testing ground’ for the principle and related views. Of course, this means that a scientific realist approach is presupposed that fills the epistemology/metaphysics gap, but is this really a problem? Should metaphysics proceed exclusively a priori? If your answer is affirmative, physics represents at least a possibility that one’s metaphysics should be able to account for. If instead one adopts the ‘naturalist’ stance, then interesting things follow. First, it is commonly believed that physics provides us with purely qualitative descriptions of the world, and that consequently we shouldn’t posit more objects than unique bundles of properties. If this is true, then if there are indiscernible but numerically distinct particles we have to either change our assumptions about PII and/or physics or move to a different ontology (your point 3), which I discuss below). (The obvious mistake, which the Hawley paper points out very well, is that a world with two indiscernibles is qualitatively different from a world with only one if properties are additive - quantum systems being ‘mini-worlds’ with additive properties. In other words, (many) naturalists seem to mistakenly infer the truth of PII from the assumption of anti-haecceitism which they make on general methodological grounds - PII does not follow from anti-haecceitism).
    A second issue, which is what I take Dmitri to be pointing out, has exactly to do with anti-haecceitism: it concerns the fact that quantum statistics is non-classical. Taking two 'quantum coins', there's only one way for them to be 'one tails and one heads', and the probabilities are (h,h)=1/3=(t,t)=(one t one h). Since classical entities (and their statistics) are paradigmatic of individuality, this is taken to indicate that quantum objects are not individuals. In this case, it would seem, anti-haecceitism does lead to non-individuality. (Here too, however (or so it seems to me) there’s room for an objection: that the statistics is permutation symmetric doesn’t *entail* that the particles are non-individuals - my opinion is, in particular, that what is non-classical are the properties, not the property-bearers). In any event, these seem to be interesting applications of certain metaphysical concepts.
    As for your 3), as far as I understand the idea is that PII doesn’t apply to absolutely everything, but only to every entity that counts as a ‘thing’ in the relevant domain. If particles are described quantum field-theoretically as ‘epiphenomenal manifestations’ of the fundamental unitary fields, they become much more ‘property-like’, and are certainly not ‘things’. Of course, on the other hand, the question of whether PII applies to fields can legitimately be asked (Muller and Saunders BJPS (2008) explicitly say this while arguing for the weak Discernibility of fermions).
    As for 2), I don’t think Adams argues for the strong form of haecceity you attribute to him. In his 1979 paper he explicitly says that he posits primitive thisnesses but doesn’t follow Scotus in regarding it as a full-blown, genuine metaphysical property. Moreover, Adams doesn’t think that his primitive thisness entails haecceitism, and in the paper he provides independent arguments in favour of haecceitism. I guess I agree with ChadC on all this. One thing I am really interested in is your claim that “The view about primitive thisnesses can serve as a foundation for arguments about transworld identity (which would be harder to make using the minimal difference position)”. Why do you say ‘harder’ exactly? I have the same intuition, but I am not sure that it makes much difference what form (Scotian haecceitas or minimal primitive difference) of non-qualitative identity one posits as long as one takes it to be a fact intrinsic to the object. Not surprisingly, naturalists who accept that PII may fail (e.g., Ladyman (2007)) still insist on ‘contextual identity’ (e.g., given by extrinsic facts about the objects’ belonging to some structure) on the basis that it is a natural foundation for anti-haecceitism. Hence, either you are suggesting that identity is primitive and contextual (is this the reason why you use 'difference' rather than 'identity'?) or one could object that you are just assuming primitive identities while rejecting primitive trans-world identities without argument. (An argument I can think of at the moment is primitive identity plus counterpart theory).

    Note on the note: ‘identical’ does have a specific meaning for physicists, having to do with sameness of essential properties (i.e., particle-kind). It is clearly unfortunate given the stricter sense of the term, but isn’t it very much what we do in our everyday language?

  10. Hi Matteo,

    I'll reply to the terminological issue first. Just to be clear here, Adams' main point about Scotus is not to deny that thisnesses are properties (for Adams, they are properties, since a thisness is a property of being identical with a certain individual: and yes in his view in some sense these are "thin" properties, not "full blown" metaphysically heavyweight ones like suchnesses). It is to deny that thisnesses are properties that are components of individuals. The difference between this view and the weaker view is that on the strong view thisnesses are properties of some sort. On the weak view, there are no thisnesses or any properties of this sort. The difference between duplicates is a primitive difference that does not consist in there being a property (or properties) or anything at all. There is just a primitive difference. That's it!

    Now, regarding transworld identity claims. If one thinks that transworld identity is determined by thisness properties, then it is easy to explain how Humphrey (he, himself) could have had one leg, even while he actually has two. If the one-legged Humphrey in W1 has the same thisness as Humphrey in @, they are transworld identical. The differences in qualitative properties between each Humphrey are not sufficient to entail they are not transworld identical. This sort of argument is not available to the fan of the weak view: here one needs extra arguments to show why objects in different worlds with different properties might nevertheless be transworld identical. There are lots of things to say, some more plausible and some less plausible.

  11. Laurie,

    It could just be a terminological issue, but I am not convinced.
    1) Given your distinction between thin and thick properties, isn't Adams thin primitive thisness as thin as your primitive difference? On the one hand, he says “Scotus regarded properties as components of the things that have them. He introduced haecceities (thisnesses) accordingly, as a special sort of metaphysical component of individuals. I am not proposing to revive this aspect of his conception of a haecceity” (1979; p. 7). On the other, one could just say that in your view objects have the thin property of 'being primitively different from other objects'.
    2) Trans-world identity: you say IF the one-legged Humphrey in W1 has the same thisness...': of course one can believe in haecceities (even thick ones!) and deny trans-world identities of this sort. As for 'extra arguments needed', as I said, Adams too claims explicitly that primitive thisnesses do not entail haecceitism.
    Anyway, I don't think this was the main point of your post...

  12. On an abundant conception of properties, there's no reason not to postulate thisnesses or haecceities as properties or property-like entities and then account for identity and distinctness in terms of having or failing to have such a property. But on a sparse conception, there are all sorts of predicates that do not refer uniquely to one property. So from the fact that we can gin up some identity predicates, it does not follow that there *are* such properties.

    A sparse-properties theorist might very well deny that identities and differences are accounted for in terms of anything property-like, whether qualitative or not, because there just aren't any such properties. Of course she doesn't have to say that (there might be sparse identity properties, depending on what account of sparseness or naturalness one gives), and of course there are other reasons she might wish to deny that identities and differences are accounted for in terms of property-like entities.

    Suppose, then, that there aren't such properties or property-like things, either for reasons of sparseness or some other reason. What, then, grounds identity on such a theory? It's primitive. Don't go looking for properties or property-like things to ground identity and difference; there aren't any such things.

    I took Laurie's weak view to be such a view. Am I in the ballpark?

  13. Jonathan,

    yes--this is the sort of view I'm talking about. I think it could use more discussion in the PII literature, since it is often overlooked.

  14. Hi all,

    A brief response to Laurie's initial three confusing things (with apologies for not having carefully read through other comments):

    (1) the philosophy of physics folk typically presuppose that physics is best-placed to tell us about the properties of physical entities; I don't think empirical indiscernibility is supposed to *entail* indiscernibility (not for everyone, anyway), but it gives us very strong reason to believe in indiscernibility.

    (2) relatedly, in this literature 'haecceities'/'haecceitism', 'thisnesses', 'transcendent individuality' etc are typically value-laden terms, associated with disreputable 'neo-scholastic' approaches to metaphysics, hence sometimes there's little motivation to stop and distinguish all these ideas carefully (though French and Krause's book is very helpful)

    (3) one potentially helpful way to think of the 'nonentities' idea is to take talk of (e.g.) bosons adverbially - some larger system behaves two-boson-ishly.

    (4) whilst I'd be delighted if everyone read my paper (Jan 09 Mind), it's just the final section which is most relevant to Laurie's concerns.


  15. Katherine,

    Thanks for this. With respect to (1), I agree that this is what the philosophy of physics people should be doing if they are being careful enough. As for (3)--I like this very much, and it dovetails with a way I've been thinking one could interpret claims about how there are two-particle systems but no facts about which particle is which. My (rough) thought is that, in some sense, we might be able to say that the fundamental entity in question is an instance of something like two-particle-system-ness, and this instance is not something composed of two distinct particles.

  16. Since Katherine has advertised the French and Krause book, which I agree is great, I want to draw attention to one way in which I think it is unhelpful. They say that individuality pertains to objects taken separately and distinguishability pertains to objects in relation to each other. I think that it is better to make the distinction between identity and diversity which pertain to the metaphysical issue of what is numerically the same or different to what, as opposed to distinguishability or indistinguishability which pertain to the epistemological issue of what is qualitatively the same or different to what (where this is supposed to be in principle empirically accessible). Individuality is then that feature of individuals associated with identity and diversity (because if a and b have different individuality they must be numerically diverse) and so pertains to objects taken both separately and collectively.

    A principle of individuation says in virtue of what it is that the relations of identity and diversity hold. PII is associated with the principle of individuation according to which all relations of identity and diversity hold in virtue of the qualitative facts. On this view, what is distinguishable from what is coextensional with what is numerically distinct from what. This collapses the metaphysics of identity and diversity onto indistinguishability/distinguishability in good empiricist style.

    It is of course open to someone to believe that if PII fails for some entities then the relevant principle of individuation must appeal to non-qualitative features of the world which might include haecceities or primitive thisness. But here is another thought: suppose one believes of a domain that PII fails and that the identity and diversity relations on the domain are not reducible to the qualitative facts that obtain it in. One might then hold that the identity and diversity relations are primitive, but still think they are not grounded in intrinsic non-qualitative properties of the individuals such as haecceities.

  17. James,

    I think you are right. I like the French and Krause book, but I was puzzled by what they meant by "individuality," partly because it seemed so different from the way that metaphysicians want to think of individuation.

  18. James,

    Sorry to insist with my comments and questions, but I would really like to fully understand your views on these matters.

    Consider a domain with only one (individual) object. In your view, the object gets its identity from the fact that it belongs to that domain (you say - elsewhere - that identity is contextual and extrinsic). Hence, it looks like there is *something* the object's identity depends on. According to another view, the object's identity is primitive and intrinsic to the object, hence it depends on absolutely nothing.

    Four questions:
    1) Is there a real difference between the two cases?
    2) If so, is something like haecceitas or primitive thisness presupposed in the second case in anything but a thin, non-metaphysically loaded sense?
    3) Is your insistence on contextuality based on anything besides your preference for anti-haecceitism?
    4) Doesn't contexutalism have the metaphysically suspicious consequence that the very same object may or may not count as an individual depending on the domain of things it belongs to?

  19. Matteo

    Thanks for your questions.

    Is there is a real difference between the case of a single object in which its identity is something to do with a structure, and the case of a single object in which its self-identity is thought to be an intrinsic matter? In that case the object is the structure so the distinction makes no sense. I am prompted to think about these matters in relation to cases where there is a non-trivial structure of individuals or objects (more on the difference or not below). (I don't think I would mind if my way of thinking about identity and diversity relations, and their relations to qualitative properties and relations, only worked for a world with lots of things and qualitative properties.)

    It is true that I have thought about things in terms of what identity 'depends on', but I am now worried about that notion (prompted by the concerns of my colleague Oystein Linnebo in the context of the mathematical structuralism debate). Cognates like the 'grounding of identity' or what an individual is itself 'in virtue of' may be thought equally dubious.

    We should perhaps focus on the notion of whether identity is definable in the logic as Saunders and Muller do.

    Anyway, I think the interesting thing, as your previous post made clear, is the connection between different principles of individuation (PII, primitive thisness or whatever), and questions about transworld identity. In the case of quantum particles and spacetime points, permuted states of a certain kind are not counted as giving rise to distinct states of affairs. The question is how to express this fact, if it is one, in terms of the philosophical logic of the identity relation. (The idea of doing so by saying that spacetime points lack primitive thisness goes back I think to Carl Hoefer and Anna Maidens.)

    2) I think your question comes down to whether or not there is a predicate like 'the haecceity of x' that refers to something different to the predicate defined p(x) iff x=a,. Is there anything more that p(x)? One way it could be more is if it supported transworld identity, and (I think that is what the tradition that reasons from the physical equivalence of permuted states to the lack of haecceities thinks.)

    3) I am not insisting on contextuality. I take Haecceitism to be the view that worlds can differ solely in the permutation of individuals. It seems reasonable to explore the possibility that the objects apparently quantified over in quantum mechanics (fermions and bosons) and spacetime theory (spacetime points), are individuated structurally and that is why permuted states, and Leibniz-equivalent models are not treated as physically distinct.

    4) I am not sure whether we should not just take 'individual' and 'object' both to be expressing just the thin notion of an object as something that is in the range of a first order variable. I suppose your question presupposes that there is a difference. But then I want to know whether individuals must persist or not, and what else it is that they have to be over and above being objects.

    I hope that makes sense. Others may be less interested in what I think than Matteo so I will stay quiet for a while now.

  20. James,

    Thanks for your reply. I agree that this shouldn't become an exchange between you and me, so I'll just make three quick points.

    1) I was taking the one object example to support intrinsic self-identity, exactly because there contextuality doesn't make sense. But you seem to accept the possibility of intrinsic s.-i. anyway.
    2) The possibility of vague objects or 'non-individuals' à la French/Krause seems sufficient for distinguishing objects that are individuals and objects that are not. Isn't this the point of Laurie's 3) and Katherine's 'adverbial talk' solution? Perhaps there just is a lack of terminological uniformity here.
    3) I see that you take a structural understanding of many-particle systems as 'a possibility to explore' in the light of permutation invariance. I thought you regarded it as an obvious consequence.

  21. I could say that properties do not "bring about" causation--rather causation is a property.
    An electified wire, when in contact with
    water, has the property of producing hydrogen and oxygen. Or, another way--you could simply say that water ---by definition-- is something which is split into hydrogen and oxygen in this way.
    There is nothing necessary about electricity nor water so interacting; being otherwise familiar with them one would not conclude
    that they would so interact. Rather it was discovered that such was the case--and that case
    added to their properties.
    Seems I have the option to include causation
    as a property or not.
    Also, what is the actor and what is the acted upon. Takes two to tango--as it were. Could say that water is acted upon--or could say that water provokes the action of electricity--that water acts upon electricity. Or could say water and electricity are two aspects of a third thing-=-production of hydrogen and oxygen--in a particular context.
    Seems to me you can parse it in several ways.
    None of it is without qualification ----only in one particular and very narrow context can it be said that water and electricity interact in this way.