We’re blogging through St. Thomas Aquinas’ Compendium Theologiae, sometimes called his Shorter Summa. Find the previous posts here.
Today’s post is from Chapter 71: “Matter Not the Cause of Diversity in Things”.
Here's a case where Thomas is ultimately right…but matters are a lot more complicated than he would have thought. He says,
The foregoing exposition shows clearly that the cause of diversity in things is not diversity on the part of matter. For, as we have proved, the divine action which brings things into being does not suppose the pre-existence of matter. The cause of diversity in things could not be on the side of matter unless matter were needed prior to the production of things, so that the various forms induced would follow diversity in matter. Therefore the cause of diversity in the things produced by God is not matter.
In Thomas' day, and in fact through most of history, the assumption was that the species of plants and animals and minerals were unchanging. They had been created at the beginning of time, and had persisted. Now we know that species have come and gone over time, and that species change over time. And presuming some flavor of Darwinian evolution (which the Church accepts) new species (in the biological sense) sure seem to arise from the action of matter.
But what Thomas means by "matter" and what we mean by "matter" are two different things; and the fact that a species of animal (the triceratops, say) came to be in time and then passed doesn't mean that the form of triceratops came to be in time. For Thomas, everything that is is a reflection of the perfection of God—and is so exactly in its form.
For Thomas, matter is that which form gives form to; and form is necessarily prior to matter because you can have form without matter but not matter without form.
Again, the plurality or unity of things is dependent on their existence. For, to the extent that anything is a being, it is also one. But forms do not possess existence on account of matter; on the contrary, matter receives existence from form. For act is more excellent than potency; and that which is the reason for a thing’s existence must be the more excellent component. Consequently forms are not diverse in order that they may befit various types of matter, but matter is diversified that it may befit various forms.
photo credit: Public Domain; source Wikimedia Commons