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.
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.
St. Thomas Aquinas. (1265-1274). Compendium Theologiae: Matter Not the Cause of Diversity in Things, trans. by Cyril Vollert. St. Louis & London: B. Herder Book Co., 1947
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