Dispositions

2. The ontology of dispositions

There are various questions concerning the ontology of dispositions. What in the world are they? Do they cause their manifestations or does something else? Are dispositions an irreducible kind? Are all properties dispositional, only some of them, or none?

If some form of the conditional analysis is correct, then according to the reductionist interpretation dispositions are not properties in their own right. The conditional analysis arguably shows that there is nothing more to a disposition than the truth of a conditional of which the antecedent and consequent may be events or states but the disposition itself is not. As a metaphysical class of existents, dispositions will have been reduced away. Armstrong thought that any such conditional required a truthmaker and that every disposition must have a categorical basis in virtue of which any such conditional is true. This suggests another possible reduction of dispositions, however, to categorical properties. Armstrong’s position is that although there is a perfectly respectable sense in which we can say that there are dispositional properties, they do not have an irreducible existence. Rather, if there are categorical properties plus the laws of nature that govern the causal relations between those properties, then having a categorical property would thereby endow something with dispositions. This is a position that has been called categorical monism or just categoricalism. The position says that all genuine properties are categorical and no irreducible property is a disposition.

A difficulty for categoricalism, however, is that the notion of the categorical is perhaps as obscure, if not more so, than that of a disposition. Rarely has the precise nature of the categorical been spelled out, while the theory of dispositions has received great attention and development in recent years. Categorical means simply unconditional. In that sense, however, dispositions are categorical. Dispositions can be possessed unconditionally as it is only their manifestations that are typically conditional on what else happens. Furthermore, if categorical really does contrast with the dispositional then does that mean that a categorical property is intrinsically powerless and disposed to do nothing? That would seem to be Armstrong’s position, which makes categorical properties endow powers only with the help of external laws of nature. If such laws are contingent, then the causal role of a property would also be contingent. This means that the same property, in other possible worlds, could have a different causal role from that which it has in our world, yet remain the very same property. This is a view that some find unacceptable. It is also regarded as problematic that categorical properties can be real while not being intrinsically causal. Such properties would violate the Eleatic stranger’s reality test, from Plato’s Sophist (c.366-360 bc), which states that something is real only when it can make a causal difference to the world. A final difficulty for categoricalism is that it is committed to there being a categorical basis for each disposition. This claim is in doubt, particularly at the sub-atomic level, where there are properties which appear to be dispositional yet for which there is no available categorical basis.

There is a position that can be called property dualism, which allows that there are dispositions as an irreducible class but that there are also irreducible categorical properties. Prior (1985) and Molnar (2003) adopt such a position. It faces two main problems. First, it relies on finding a reliable distinction between the dispositional and categorical, which as we have seen above is difficult. Molnar tries to argue that the non-dispositional properties are mainly the spatial properties of location and orientation. But this means he has to argue that although they are not causally powerful, they are nevertheless causally relevant and thus satisfy the Eleatic stranger’s reality test. The second problem with dualism is that we require an account of how dispositional and categorical properties relate. If one is to say that dispositions have categorical bases, yet are distinct from their bases, then one has to face the question of whether the disposition or its categorical basis is the cause of the manifestation, when the appropriate conditions are realised. Either answer raises difficulties, as does the compromise that both the disposition and its basis cause the manifestation together.

A third main position can be called pan-dispositionalism, which is the view that all properties are dispositional. Shoemaker (1980) reintroduced this view in modern times. The position has the advantage of allowing all properties to be intrinsically powerful. The Eleatic stranger’s test is thereby passed. The causal role of a property is essential to it and cannot vary across possible worlds. Some see this as implying that the laws of nature are metaphysically necessary, but another interpretation is that they are metaphysically redundant. There is also no problem of explaining a relation between dispositions and non-dispositions.

Among the difficulties of this position, however, there is an alleged regress. A disposition is a disposition to do something else. But if all properties are dispositional, then this something else must also be dispositional. A disposition is always therefore a disposition to a further disposition, which in turn is a disposition to a further disposition. This has produced the charge that nothing would ever pass from potency into actuality.

Despite their diversity, all of categoricalism, dualism and pan-dispositionalism remain live options, all with their advantages but considerable disadvantages. There is a further question of whether the three ontologies exhaust the possibilities. One recent view is that while there is a dispositional-categorical distinction, there is not a corresponding division in reality between properties (Mumford 1998). This may mean that none of the three main ontological options is right.