Something about Aristotelean-Thomist (A-T) metaphysics bothers me, and Jon Garvey reminds me of it again in a recent post.
He says above “substance” has to do (in A-T thought) with form.
To me, this is an abuse of language and of all metaphysical intuition!
Normally, we say thing is 'substance in a form', or a thing is made out of some substance and is arranged in some form. So 'substance' and 'form' are combined (metaphysically) to make a particular thing. A substance can be arranged in many possible forms, and a given form may be made out of many possible substances. But, if we specify substance and form, then we specify a thing.
But, as Jon points out, this natural way of speaking is completely up-ended in A-T language. There 'substance' and 'form' are practically identified! They are of course completely allowed to define words how they like. But, if I were starting a new metaphysics suitable for science, that is NOT how I would proceed. It is completely bizarre!
In fact, Aristotle bears some responsibility for this. He talks of things made of matter, and then 'form' as 'everything else that makes a thing what it is'. But that leave unclear how causal powers of thing are supposed to exist: since they are not matter they must be form. This conflates (in a stupid way) the ideas of 'form' as structure and 'form as causal power'.
Then Aquinas bears further responsibility. He sees the above problem. He wants to attribute causal powers to substance (a good idea, I say). But, rather than fixing Aristotle's definition of 'form', he then conflates (in a stupid way) the ideas of 'form' and 'substance'. He has no option left. But that results in the idea of a 'substantial form'. That might be ok, except (as I point out just above), any clean new metaphysics would distinguish 'substance' and 'form'. A-T is not clean in that respect.
Essence is that which makes something what it is.
Substance is that out of which something is made.
The format of Thomistic metaphysics then takes a somewhat dyadic structure of descending generality: (i) essence and existence, (ii) substance and accident, (iii) matter and form.
http://www.iep.utm.edu/aq-meta/ (much good Thomist presentation!)
In general, we can (must!) diverge from materialism. We can be guided by Aquinas’ insights, not to mention more general Christian insights. But that does not mean necessarily following the A-T system in all its glorious details. Instead, see my previous post for what a new kind of metaphysics could be that talks properly about substance and form.