Scientific analyses of powers or dispositions
Consider how science might analyze the fragility of a glass vase, namely the disposition to break after small external pressures. The very first analysis would be to treat the vase as a whole with mass, shape, rigidity and fragility. The fragility is then a property of the vase. The vase is therefore an object with specific dispositional properties and, as well, with a shape and orientation. The second analysis would be to consider that the vase is made of glass, where the glass is a continuous solid with various mass, elastic and fracture properties. A computer finite-element model of the vase might then explain its fragility in terms of the stress and fracture properties of the constituent material. In this case, the glass is the dispositional material, to be arranged in the shape of the vase and thereby to explain the properties of the vase. A third level of analysis might be a molecular simulation, where elasticity and fractures are properties derived from the strengths of interaction potentials between molecules. Now, the molecules are the objects constituted by those interaction potentials, which are dispositions, and they are arranged to make macroscopic glass-material. And so on: a fourth level may consider the potentials between individual electrons and nuclei, where now those electrons and nuclei are constituted by mass, charge, spin, magnetic moments, etc.: all dispositional properties. Surely quantum mechanics is also needed, which introduces its own set of probabilistic dispositions (propensities).
We see that at each stage of microscopic analysis, the presented objects are diagnosed as structural forms of some more fundamental disposition. Whether the stages reach the most fundamental level is not the issue here. Rather, at each level, the result of the analysis is to attribute existence to some ‘stuff’ with some causal powers held essentially. First, the vase as a whole was the existing stuff; in the second analysis, the glass with stress-strain powers is taken as the stuff of the vase; later it is electrons, etc., with electric charges; and the final stage listed here has electrons with propensities to emit or absorb virtual photons.
The attribution of dispositions in all of the above cases is according to the following logical template:
“Object S has the disposition P to do action A” is equivalent to “if S is in some circumstance C, C depending on P and the character of A, then there will be a non-zero likelihood of S doing A”.
For example, “A vase object has the disposition to break" is equivalent to “If the vase is in some circumstance of being struck forcefully, this circumstance depending on the precise fragility and the character of the breaking, then there is a non-zero likelihood of the vase breaking".
New Ontology for Substance
We thus see 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.