Transubstantiation is in the news. For reasons I have not investigated, the Vatican has decreed that you can’t transubstantiate gluten-free bread. Or that you ought not.
Maybe it is possible. It should be possible, actually, according to the theory, as I understand it.
If you believe in transubstantiation, then here is how you can explain it.
First you have to have matter and form. So far, so Platonic. The Aristotelian twist is that substance is not exclusively formal, but requires matter. So you have matter and form to make the substance of bread. But beyond that you have to have accidental and substantial forms. Accidents are not material, they also are formal. (Matter needs form to be encountered at all, actually.)
So, you can change the accidents on a thing without affecting what it essentially is. You can have barley bread, wheat bread, black or white bread, long or short bread, etc. It is all bread–bread is the basic substance. You can change the accidents, but not the substance: it is still bread. You can change, therefore, the accidental forms supplying that lump of matter with its peculiar characteristics. But if you change the substantial form you’ll get a different substance.
Matter and form account for change. What is the difference between a corpse and the body of a living human? In Aristotle’s irreverent, scientific philosophy, a change in substantial form. Matter is the same, but the form is different. Accidents remain: weight, quantity (one body), color and such. Accidental forms are not necessarily changed, though they’re mutable and may, but substantial form does change in this instance.
So you can change the accidents on a thing, you can switch out the form, but what does not naturally occurr is when both matter and form united (which is substance, as opposed to substantial form), when both matter and form, I say, change at the same time. That is transubstantiation.
Luther thought this was wrong because you lost the bread. He believed the body of Christ was present after consecration, but so was the substantial bread. I suppose he posited two substances in one place. Aquinas, on the other hand, explains that the only part of the bread remaining are accidents: weight, number, volume, color, smell. Another substance occupies that place. Since an effect cannot exceed its cause, the cause that brings about the change of matter and substantial form does not affect the accidental forms. It does not aim to change them, that would be horrible. So the accidents have no reason to change; all the contrary.
Gluten-free would be an accident. Can the body of our Lord cannot have such an accident? Is that what they’re thinking? Makes me wish I were still in class at Villanova. I’d probably learn it was a decision NOT left up to Thomists and therefore a bad, incompetent promulgation.