Dispositional InEssentialism's Implausibility

Given dispositional realism, there are two main positions taken in the debate on whether or not dispositions are essential to their bearers*:

Dispositional Essentialism: Dispositions are the 'what it is to be' for the objects that have them and the existence of these objects is conditional upon their having these dispositions. An object having different dispositions than the ones it does is therefore impossible. Thus, different laws of nature, different objects. (Bird, Ellis & Lierse, Marcus)

Dispositional InEssentialism: Dispositions are contingent aspects of the objects that have them and the existence of these objects is not conditional upon their having these dispositions. An object having different dispositions than the ones it does is possible. Thus, different laws of nature do not imply different objects. (Armstrong, Lewis)

Now, importantly, the debate about dispositional essentialism is a debate about so-called fundamental entities; those 'natural' objects of scientific enquiry - quarks, leptons and electrons. The exemplar question is something like 'Is it possible for an electron to attract another electron'? - ie. could the dispositional nature of an electron have been different?

For the dispositional inessentialist, an electron possibly attracting another electron is accounted for by the fact that the laws of nature are contingent - the 'Contingency Thesis'. And since different laws of nature holding amounts to there being different ways things must act, it is possible that things have different constraints on the way they interact with one another and hence, different dispositional natures.

The problem with this view, I think, have been laid-out fairly successfully by Bird in his Nature's Metaphysics. For one, laws of nature understood as either regularities or nomic-necessitation generalizations both seem untenable; I won't go in to the intricacies here - suffice it to say that regularities supervene, not impose themselves on objects and nomic-necessitiation is seemingly ad hoc logic-chopping. And since an account of dispositional inessentialism entails that the laws of nature are extra-objectual and no such account of laws is plausible, neither is dispositional inessentialism.

Secondly though, and more importantly, is the charge that if the laws of nature are understood as extra-objectual (as I claimed that dispositional inessentialism presupposes), then one must be a quidditivist about properties. That is, one must hold that the dispositional nature of any property is not essential to it. Why is the dispositional inessentialist committed to property quidditivism? Firstly, she is an extra-objectual law theorist - so the laws of nature must determine dispositions, not vice-versa. Secondly, she must accept the following proposition:

(ep) An electron could be a positron.

Now, the dispositional inessentialist will protest: I would not dare say that an electron could be a positron! Rather than accepting (ep), I am making the weaker claim that an electron might have had the disposition to attract other electrons - ie. it could have been positively charged. I am not then, as you are claiming, attempting to make the claim that one kind of entity might have been another fundamentally different kind of entity - surely this is absurd.

But what does the acceptance of (ep) entail? Consider that an electron and positron share all of their structural properties and differ only in the value of their charge. The claim made by (ep) is then not simply that an electron could have had a positive charge. This is because, ex hypothesi, a positron just is an object having all of the structural properties an electron has and being positively charged. So the dispositional inessentialist is committed to (ep) afterall.

You might wonder what accepting (ep) has to do with property quidditivism, since the former concerns entities, the latter properties. But I suggest that the claim that the property 'being negatively charged' might have had the role of attracting negative charges is precisely the mistake that the dispositional inessentialist makes. Why? Because 'repelling negative charges' simply is what it is to be a negative charge. Similarly, 'being negatively charged' simply is what it is to be an electron. So, being a dispositional inessentialist entails the acceptance of (ep). And since (ep) is absurd, so is dispositional inessentialism; and, for that matter, property quidditivism.



*There is another, somewhat middle position that Mumford takes, which I call 'soft dispositional essentialism', according to which objects have their dispositions essentially, but their dispositions are relative to a world. Under soft dispositional essentialism, it is possible for an object to have different dispositions, but not different world-indexed dispositions. This account preserves the Contingency Thesis and dispositional essentialism, but is ultimately unacceptable. In short, it can't be claimed that an object such as an electron has different world-indexed dispositions since, as I suggest, what it is to be an electron is to have a particular dispositional nature. Therefore, any object with a different dispositional nature is conceptually barred from being an electron and so no electron could have different dispositions than the ones it does.