A Thought Experiment against Humean Supervenience: Conceivability & Intuitions

One thought experiment that objectors against Humean Supervenience are quick to suggest is that of two possible worlds which both contain only one existing material object that always moves in a constant velocity. The thought experiment goes: in the first world, the particle is governed by the law that all particles move with constant velocity and in the second world, the particle is governed by the law that all particles obey Newton's Second Law; in other words, in the second (and not the first) world, if another particle had existed there, they may have had an effect on one another's velocity.

Is this a good counterexample via thought experiment? In a recent paper, Ned Hall tries to construe this counter-example as relying on the 'Conceivability entails Possibility' principle. And he therefore dismisses it. It is certainly true that the set-up of the thought experiment involves the (C-->P) principle, insofar as it must be committed to it being possible that there could be a world with only one particle and a world differing from another in only its modal facts.

But although I whole-heartedly dismiss the (C-->P) principle, I'm not so sure that a counterexample wherein two different objects in two distinct possible worlds are intrinsic duplicates and yet differ in their nomic-profiles is to endorse a possibility only on the basis of conceivability. Why is this such a leap in conceivability? I think the non-reductionist example is meant to (or at least, should aim to) exploit a seperate intuition; not the C-->P intuition. The intuition is: how a particular object (or kind of event) has been, is, or will be says nothing about ways it might have been.

It won't do to simply dismiss the non-reductionist thought experiment on the basis that it assumes that one world could differ in its laws while another one does not. For while this is assumed, and while it is an assumption that tips the scales, so to speak, it is not an altogether unwarranted assumption. And the onus is on the Humean to explicate the ways in which this thought example goes wrong. It won't be enough for the Humean to claim that the two worlds differing in their Laws is just impossible, any more than it will do for the non-reductionist to claim that it is possible. The non-reductionist position exploits an intuition, one that, for all I can tell, is fairly plausible, while the Humean position combats this intuition, but with no reason other than the fact that it does not accord with his theory.

On 'The Limits of Contingency' & Metaphysical Possibility

An article by Gideon Rosen entitled 'The Limits of Contingency' recently peaked my interest. Rosen makes an interesting distinction between two conceptions of metaphysical possibility - what he calls Standard and Non-Standard. According to the standard conception of metaphysical possibility, a property P is possible for an object x iff P can be possessed by x in a world whose 'form' is the same as the actual world. By form, Rosen means something like the fundamental laws of how objects are composed or how causation goes about - something broadly like 'ontological rules'. According to the non-standard conception of metaphysical possibility, a property P is possible for an object x iff P is logically coherent with the 'what it is to be' of x. That is, only if P does not logically conflict with x's 'individual nature'.

The first thing to notice is that the standard conception requires a certain checking against the conditions of the actual world - a position which I think represents a respectful speculative sobriety. The non-standard version of metaphysical possibility only requires that a property be compatible with the 'nature' of an object and presumably, since an object's nature might very well be intact while it does not exist in the actual world (think Plantingian Essences or Platonic Divine Idea Essences), metaphysical possibility is not constrained by the conditions of the actual world.

I think that the two positions - the standard and non-standard - are, as Rosen claims, very common notions of metaphysical possibility. Those who think that sortals are the de re governors of what is metaphysically possible for an object clearly fall into the non-standard camp, though this seems a rather standard position in modern philosophy. And those who think that metaphysical possibility has something to do with the laws of the actual world will, in most instances, fall into the standard camp; those who do often want to identify metaphysical possibility with physical possibility, broadly construed.

At the risk of being philosophically trite, my sentiments lie with the middle position. In general, I think that the non-standard version is correct - metaphysical possibility must be de re in a significant sense and this sense must have to do with the 'nature' of the object in question. On the other hand, however, the non-standard conception does not appropriately respect the privileged status of actuality - there are no merely possible worlds over which we might peer out and look down upon to inspect the natures of the objects within. Any considerations that we have of this kind - where we think we have real knowledge of the modality of non-existent objects - seem to me to be based solely on our powers of conceptualizing, not on the nature of these objects themselves.

Metaphysical modality, I think, must be about objects and so must also be about their 'definitional natures', but it cannot merely be a matter of logical non-contradiction without consideration of the actual world. On the other hand, it equally cannot concern the 'form' of the actual world, except insofar as 'form' is taken to mean the natures of the objects within it.

On Aristotelian Actualism

Here is an interesting appellation for a philosophical position! The initial question is: how could any philosophical tenet which claimed in any way to be Aristotelian fail to have actualist commitments? Aristotelian Actualism has such commitments in the expected way - this brand of actualism states that there are no de re modal facts about non-actual objects - ala Adams in 'Actualism and Thisness'. I find this claim theoretically sound - if one is an actualist that is. However, interestingly enough, note that even if one is a possibilitist, one still does not grant a modal profile to non-actual objects since, for the counterpart theorist (excepting here Paul perhaps, though I yet find her position to fall back into straight Lewisian counterpart theory), no object in and of itself has any modal features; not just the indexically-picked 'actual' objects of our world - but none simpliciter.

The more important claim of Aristotelian Actualism however, is the following: what is possible might have not been possible - or, put in another way, there are things which are not possible but which might have been possible. This claim stems from the facts that (i)no non-actual object has a modal profile and (ii)which world (and objects therein) is actual is a contingent matter. But if this is the case, how do we secure the modal claims which involve quantification over non-actual objects and their de re character? In his 'In Defense of Aristotelian Actualism', GW Fitch suggests that we use Adams' 'truth-at-a-world' distinction - these objects do not have a modal profile, but if they were actual, they would.

Now, as an actualist, I find the claim of Aristotelian Actualism intuitively plausible. But I do have a certain qualm with it - it must rely on the accessibility relation. I am deeply committed to an S5 system of modal logic wherein what is possible is necessarily possible - and this is something that the Aristotelian Actualist must deny. But must an actualist simpliciter deny it? I think not; Plantinga, to the extent that he is, as he claims, an actualist, accepts an S5 system of logic.

Firstly then, note that the accessibility relation that is said to hold between possible worlds collapses into incoherency when we note that each possible world contains every other in the following sense: what is possible in W is, no matter what world happens to be actual, still possible in W.That is, every possible world, being abstractions from the concrete world, contains facts about every other possible world. So certain facts about some object which exists in W, but not in W2, still are possible 'from' W2, since the object would have existed were W actual - and there are, furthermore, definitive facts about that object's existence in W2. So, the tenet that Aristotelian Actualism holds which rests upon the accessibility relation is incoherent because any object that is a possible existent is a possible existent 'from' any possible world; admittedly, there is a certain sense according to which certain objects are not possible from certain possible worlds, but this is not possibility per se, but rather some attenuated form of physical possibility.

How can one be an actualist and yet claim that there are certain de re facts about non-actual object? Well, firstly, I think that an actualist has a strong commitment to the denial of non-actual objects. But I also think that the actualist ought to have an equally strong commitment to the sufficiency of the concrete world to provide the basis for any and every object which might exist - that the furniture of the concrete world is large enough to seat any and all modal profiles of any possibly existing objects. This being said, I agree with the Aristotelian Actualist that there are no, as Mondadori puts is, distinct possibilities for non-actual (read: non-existing) objects, but I do not agree that when these objects come into existence, something is made possible which was not already so. Non-actual objects do have full modal profiles, but they are simply not 'present' in the concrete world.

This is the intuition behind the claim that, if these objects were actual, they would have such and such modal profiles. In other words, there is a definitive fact about non-actual object's modal characters, but it is a fact which is yet to obtain. There are, as Adams might put the matter, no propositions with them as constituents, but there would be a definitive set of such propositions, should they come into existence.

In short, I agree with Aristotelian Actualism to the extent that it claims that de re modal characters are applicable only to actual objects and that all other possibility claims about non-actual objects are merely 'generic'. But I do not agree that, had some other world been actual, and some other set of objects actual, that there would be things possible that were not previously. Rather, these de re distinct possibilities were always possible, since the objects themselves were always so, but they are now 'attainable' on account of them being present in the concrete world.

Concretism and Abstractionism: Grounds of Possibility

What exactly is the character of possible worlds and, more importantly, whence the ground of possibility for objects?

There are essentially two paths one might take of the character of possible worlds: concretism and abstractionism. The concretist, ala Lewis, understands possible worlds to be maximal collocations of spatio-temporally related objects. The abstractionist, ala Adams or Plantinga, understands possible worlds to be maximally consistent sets of propositions or states-of-affairs. Notice then that the abstractionist holds that there are two sorts of things in the Universe (where the term 'Universe' means the entirety of reality) - possible worlds and a concrete world to which these possible worlds might 'match-up'.

So, the concretist believes that all worlds are, so to speak, on the same playing field - each is just as 'real' as every other; hence the concretist's inherent commitment to an indexical analysis of actuality. The abstractionist however, believes that one possible world is privileged - only one world happens to match-up to the concrete world; of course, concretists have no need to have anything 'match-up' to anything else.

What then are these two conceptions' respective theories of the foundation of de re possibility? The concretists founds the de re possibilities of an object in its counterparts - those objects in different possible worlds which are qualitatively similar to the object in question. What makes it possible that an object x have a property P (one which it doesn't actually possess) is the fact that y, a qualitatively similar (but necessarily distinct) object existing in another possible world actually does have P.

The abstractionist, on the other hand, founds the de re possibilities of an object in a proposition which expresses a state of affairs containing the object actually possessing the property in question. What makes it possible that x possess P is that there (necessarily) exists a proposition which is part of a possible world of the form 'x has P'. This proposition being a part of a possible world just means, as Plantinga states, that if this possible world were actual (that is, if it did in fact match-up to the concrete world) then it would be the case that x would have P.

Now, although I think that there are plenty of problems for either view of possible worlds - I want to point out two pertinent ones here which I think go directly against our intuitional common sense.

The first is, why should we agree that the fact that some other object, wholly distinct from x and only related to it by way of it being merely qualitatively similar to it in certain respects, in virtue of it standing in some closed spatio-temporal relation to some other objects in another fully concrete world has any say whatsoever in the de re possibilities of x? The question is not the familiar objection to counterpart theory - namely "What's he got to do with me?" (though I think this is a valid and pertinent objection). Rather, the question is - what has concreteness and qualitative similarity in a counterpart have to do with grounding modal facts about objects?

Secondly, concerning abstractionism, why should we agree that a proposition in a 'Platonic Heaven' has any fundamental role in determining which things are possible for an object and which are not? The abstractionist seems to me rather to have things the wrong way around - it is the objects in the concrete world and their dispositional properties therein which ground whether or not there exist such propositions expressing states of affairs wherein they possess some certain property.

Besides this, why should we agree, with the abstractionist, that propositions which do not match-up with the concrete world even exist in any form whatsoever? Now, Plantinga certainly has independent motivation for holding this brand of abstractionism - his actualism entails, he thinks, the need to have an 'essence' which grounds the fact that there are propositions about non-existent individuals. But I am inclined to think, with Adams, that there are no singular propositions about non-actual individuals - these propositions supervene on actual existents. And I am also therefore inclined to think that propositions about an object x possessing a property P 'exist', but not, as it were, pre-objectually or extra-objectually.