All change presupposes a subject of change.
Causality is a change.
Causality presupposes a subject of a change.
But to presuppose some subject is not to cause it, and so it is false to say that the ultimate natural subject that changes from this to that is caused. The subject is natural because a subject of change is nothing but a changing subject and so if the end result is natural, the subject is too.
Schopenhauer’s argument does a particularly good job at isolating the Kantian idea that, (to put it charitably) even if God could cause the world, it would be a very different sort causality. Everyone understands the sort of causality of, say, one thing pushing another or one hot thing making something else hot, but the sort of causality that terminates a cosmological proof is a very different thing. Thomists can often play too loose with the idea of God being a “cause of being” or even “the first in an order of subordinated causes”. Do we even see these sorts of causes?
A larger problem is that the cosmological proof appeals to the idea that univocal causes are caused by equivocal ones – but whereas St. Thomas and Aristotle set forth very clear instances in nature of equivocal causality, most have fallen with the old physics. No one thinks, say, that “man comes from man and the sun” – by which Aristotle meant that, though John might generate John Jr., it was the sun that generated man as man, and thus contained within itself all the perfections of man, though in a higher way. Equivocal causes were once, quite literally, as plain as day. Anyone could just look to the sky and see them. But we cannot see them any more, and even if we could, we would not see them in the heavens. In effect, Schopenhauer’s argument in Thomistic language is much briefer:
All causes are univocal.
Cosmological arguments require non-univocal causes.
There is more than one response here.
1.) Causes as such do not depend on a subject, since causes as such don’t depend on anything. To depend on another to exist is to be an effect, and no cause as such is its contrary. The conclusion of the first argument we gave is therefore not necessary, and if the major is true the minor is false.
1a.) As a corollary, the divine causality most of all satisfies the notion we have of a cause. Because casuality by nature is distinct from dependence on another, and whatever requires a subject to cause depends on it, then a cause which presupposed no subject in its causal action would most of all satisfy what we mean by a cause.
Whatever one might learn from Schopenhauer, ther is one thing that needs to be utterly rooted up and thrown out – his judgment of metaphysical thing by the imagination. The sense that causes need some subject on which to act does not arise from considering them as known, but from false imagination. It is the cause as imagined that needs a subject or must be always univocal. Judged according to intellect – that is according to the intelligible notion of causality – the need for a subject is a deficiency or imperfection of causal power.