I have for a long time now been very dissatisfied with the metaphysical categories bequeathed to us from Aristotle via a multitude of commentators and philosophers ranging from Boethius to Ockham to Locke to Hume to Kant. It seems to me that they are based on a prescientific notion of what sorts of things exist. In particular, the notion of substance strikes me as questionable: it is based rather explicitly on the distinction between the clay a potter uses and the properties of a particular piece of pottery. By starting with a human-centric activity, Aristotle inverted the way things are: thinking that because humans impute – in this case social and cultural – properties to some objects by forming them, this must be true of all things. There is no reason now to think that the universe is somehow dependent upon human categories.
Moreover, the substance doctrine, which reappears in Locke as primary qualities, in medieval philosophy as first intention, in Kant as the noumenal, and in modern philosophy as categoricals, is devised to oppose the atomist doctrines that competed for attention through Democritus and Epicurus at the time Aristotle was writing. The failure, then, of atomism is due more to the lack of empirical evidence than the failure of the metaphysics it implied. And of course we know a lot more about the physical world now than then. So, why hang on to “substance”?
Epicurean atomism held that the properties of objects were the sum of the properties of the constituents (the atoms). This constitutive metaphysics was rejected not only by Aristotle but by Christian, Jewish and Islamic philosophers right through to the modern era. One of the first things Darwin was accused of was being Epicurean. Oddly, however, when the Catholic Church revived Thomistic Aristotelian philosophy in the 1870s, their first target was not Darwin, but Daltonian (that is, atomistic) chemistry. And that makes sense when you realise that the doctrine of transsubstantiation in the Mass (that the outward form, or species of the bread and wine remain the same while the substance is changed into the substance of Jesus’s body and blood, which is at best a confusion of Aristotle’s metaphysics) relies on the notion of substance that chemistry basically removes the need for.
Of course, the notion was (forgive me) substantially revised to be consistent with the new chemistry and physics, but in doing so the concept became as vague and confused as it can be. And philosophy has been trying to deal with that ever since.
The basic reason for substance talk is that there needs to be something to bear the properties. That is, the reason why those properties are part of that thing and not some other thing with the same properties is that they exist on a different substance. On the atomistic account, the properties are those of the constituents working together. There is no need for substance because the atoms are the individuating objects. Likewise there are no need for external universals either – one atom is the same as another (on the classical view).
Of course, we have changed our understanding of atoms a fair bit since Democritus: Dalton pointed out that atoms come in different kinds; Bohr that atoms are not indivisible, and that there are further particles that give them their properties, and so on. But there’s a problem, which I heard in a rich and complex talk yesterday by PhD student metaphysician Sharon Ford: underneath these are fields, not particles, and fields seem to be the wrong kind of thing to bear properties. Sharon has a solution that I won’t even try to repeat here, suffice it to say she applies Minkowskian worldline models to generate persistent objects and extended objects from gauge bosons. That’s about all I understood.
My point is that we need to start a new metaphysical set of categories based on (what else?) the best of our current science, not repeat the categories based on the prescientific musings of those who thought knowledge resided in definitions of words. As support, I quote from Leibniz in the New Essay on Human Understanding (1996 p319) (Philolethes is Locke, Theophilus is Leibniz):
PHIL. §25. Languages were established before sciences, and things were put into species [logical categories - JSW] by ignorant and illiterate people [cf. Locke's Essay Bk III, chap. 6, §25].
THEO. This is true, but the people who study a subject-matter correct popular notions. Assayers have found precise methods for identifying and separating metals, botanists have marvelously extended our knowledge of plants, and experiments have been made on insects that have given us new routes into the knowledge of animals. However, we are still far short of halfway along our journey.
Dare I say that we are now much more than halfway? The sciences we have now play with the fundamental properties of the universe. We are on the verge of recreating the forces that generated the material world. Surely that is a better basis for metaphysics than sitting in an armchair and reflecting on the experience of an Oxford Don or an ancient Greek. Down with substance, I say, and everything that depends upon it!