4.4 Dispositions in nature

This dispositional essentialism leaves two important questions still unanswered. The first question is whether all, or only some of an object’s properties are dispositional. We would naively think that structural properties such as shapes, sizes and arrangements of parts are not dispositional properties, but Bird (2005b) argues that we cannot be sure of this. It would be useful to have a clear understanding of how (or whether) dispositional and non-dispositional properties can be simultaneously instantiated in an object. The second question concerns ontology: what is the relation between dispositional properties and the being (or substance) of the object with such properties? Menzies (2009) doubts, for example, that properties can be correctly construed as causal powers. Surely, he says, it is objects rather than properties which are the correct bearers of enduring causal powers.

In the previous section, we saw how science analyzes and constitutes dispositional properties and how those properties are explained as forms of some essential more-fundamental dispositions or propensities. We can now philosophically generalize that analysis in order to formulate a new view of the constitution of objects, such that dispositional essentialism logically follows. This new constitution is to take powers or propensities themselves as the persisting ‘stuff’ of which objects are made. That is, I argue that we should identify ‘propensity’ and ‘substance’ so that natural objects, as ‘forms of propensity’, are then ‘forms of a substance’ in nearly the manner of Aristotle.

It is admittedly a large metaphysical leap to identify propensity as substance, but I will argue that the identification is grammatically correct, philosophically sound, historically defensible, and physically correct, and that it even helps clarify interpretations of quantum physics. It furthermore agrees with the Eleatic Principle: that existence should only be given to that which has causal power. In a more modern age, this would be called a ‘pragmatic’ view of substance, as attributing significance not to what something merely is but to what it can do. The identity of substance and propensity is claimed in the same sense that, while the morning star and the evening star are initially known independently, they turn out to refer to the same (ontological) being. This identification should be the next development for those who adhere today to dispositional essentialism. Instead of worrying about ‘ungrounded dispositions’, we will see that dispositions are able themselves to be grounds or bearers of properties.