Thomas Aquinas on spiritual matter

Many thirteenth-century theologians believed that even spiritual beings contained matter (Spade 2008). They called the matter of spiritual beings "spiritual matter" to distinguish it from corporeal matter. Thomas Aquinas rejected spiritual matter, going against what was probably the majority opinion. In this essay, I examine Aquinas's reasons for rejecting spiritual matter.

1) Misconception: Aquinas equated matter with corporeality

A number of authors claim that Aquinas regarded "spiritual matter" as a straightforward contradiction. Joseph Magee (1999) writes, "For Aquinas, the idea of spiritual matter was a complete confusion. If a thing is spiritual, then, insofar as it is spiritual, it is not material in the sense that it is not composed of matter."[1] Armand Maurer (1968, 20-21) flatly states that Aquinas "regarded the notion of spiritual matter to be a contradiction in terms". David Keck (1998, 99) explains (and endorses) the assumption behind this claim: "For Aquinas, matter is equivalent to corporeality."

As far as I can tell, this claim doesn't hold up. Unless Aquinas was a much worse Aristotelian than we normally think, he couldn't have equated matter with corporeality.

Following Descartes, we moderns generally use the word "matter" to refer to a fixed category of substances, namely corporeal substances. In contrast, thirteenth-century theologians used "matter" in a more Aristotelian sense.

For Aristotle, "matter" (hyle) is a relative term (Physica 194b9), not a label for a fixed category. The question is not "Is X matter?" but, rather, "What is X's matter?" Aristotle explains that matter is potentiality (De Anima 412a9). Thus, we can define matter as follows: M is X's matter if and only if M has the potential to be X.[2] For example, a bronze sphere's matter is its bronze.

If we understand matter in this way, then there's no a priori reason why only corporeal beings should have matter. To say that X has matter isn't to say that X is corporeal; rather, it's to say that there's something that's potentially X.

2) Aquinas's real reasons for rejecting spiritual matter (Summa Theologiae 1.50.2)

2.1) Prime matter

Aquinas's real arguments against spiritual matter can be found at Summa Theologiae 1.50.2. To understand the first argument, we must understand the concept of "prime matter".

The counterpart of matter is form. While matter is potentiality, form is actuality (De Anima 412a9). X's matter is potentially X; X's form is the property that makes X's matter actually X. If a bronze sphere's matter is its bronze, then its form is its roundness.

If you abstract away the form of roundness from a bronze sphere, then you're left with the matter, i.e. bronze. The bronze has its own matter—the copper and tin from which the bronze was made.[3] However, if you keep stripping away forms, then you eventually reach a point where there are no forms left. What's left? What Aristotelians call "prime matter" (Latin prima materia). Prime matter is the basic stuff that every other material thing is made of.

2.2) The first argument against spiritual matter

Aquinas first argues that "there cannot be one matter of spiritual and of corporeal things". The best way to figure out what this means is simply to look at the argument.

The argument has two parts. Here's the first part:

"It is not possible that a spiritual and a corporeal form should be received into the same part of matter, otherwise one and the same thing would be corporeal and spiritual. Hence it would follow that one part of matter receives the corporeal form, and another receives the spiritual form."

If we fill in some of the missing premises, then we can parse the reasoning as follows:

1. If a portion of matter receives a spiritual form, then it becomes a spiritual thing. (Premise)
2. If a portion of matter receives a corporeal form, then it becomes a corporeal thing. (Premise)
3. One and the same thing can't be both corporeal and spiritual. (Premise)
4. Therefore, one and the same portion of matter can't receive both spiritual forms and corporeal forms.

Here's the second part of the argument:

"Matter, however, is not divisible into parts except as regarded under quantity; and without quantity substance is indivisible, as Aristotle says (Phys. i, text 15). Therefore it would follow that the matter of spiritual things is subject to quantity; which cannot be. Therefore it is impossible that corporeal and spiritual things should have the same matter."

This can be parsed as follows:

1. If a portion of matter receives a spiritual form, then it becomes the matter of a spiritual thing. (Premise)
2. Matter is divisible into portions only if it has quantity. (Premise) 
3. The matter of a spiritual thing can't have quantity. (Premise)
4. Suppose that one portion of a lump of matter receives spiritual forms and a different portion receives corporeal forms.
5. Then the portion that receives spiritual forms must have quantity. (2, 4)
6. Then the matter of a spiritual thing has quantity. (1, 5)
7. Contradiction. (3, 6)
8. Therefore, it's impossible for one portion of a lump of matter to receive spiritual forms and a different portion to receive corporeal forms. (4-7)

So spiritual forms and corporeal forms can't both be received into a single lump of prime matter—either into the very same portion of that lump or different portions of it. Now we can understand what Aquinas means when he says that "there cannot be one matter of spiritual and of corporeal things": spiritual and corporeal beings can't have both been made from the same prime matter.

Notice: this doesn't mean that corporeal beings and spiritual beings can't both have matter. It doesn't even mean that they can't both have prime matter underlying all of their forms. What it means is that God couldn't have created spiritual and corporeal beings by starting with prime matter and then giving it spiritual and corporeal forms.

2.3) The second argument

The second argument is meant to rule out any kind of matter at all in spiritual beings:

"It is, further, impossible for an intellectual substance to have any kind of matter. For the operation belonging to anything is according to the mode of its substance. Now to understand is an altogether immaterial operation, as appears from its object, whence any act receives its species and nature. For a thing is understood according to its degree of immateriality; because forms that exist in matter are individual forms which the intellect cannot apprehend as such. Hence it must be that every intellectual substance is altogether immaterial."

Here are the assumptions behind this argument:

• Spiritual beings are pure intellects, i.e. a spiritual being has no part that is not an intellect.[4]
• One understands only universals.
• Understanding X involves receiving X as a form.
• If something having matter receives a form, then the form is not (or ceases to be) universal.

The last assumption rests on the Aristotelian principle that matter individuates forms. For example, a bronze sphere's bronze individuates the bronze sphere's roundness: it's no longer the form of roundness in general; rather, it's the roundness of this particular bronze sphere.

The argument can be parsed as follows:

1. A spiritual being has no part that is not an intellect. (Premise)
2. One understands only universals. (Premise)
3. Understanding X involves receiving X as a form. (Premise)
4. If something having matter receives a form, then the form is not (or ceases to be) universal. (Premise)
5. An intellect can understand. (Analytic truth)
6. An intellect can understand universals (2, 5).
7. An intellect can receive a universal as a form (3, 6).
8. An intellect cannot have matter (4, 7).
9. Therefore, a spiritual being has no part that has matter (1, 8).

I personally think that this argument is unsound. I reject premise 3: I don't think that understanding X involves receiving X as a form. Rather, I think that understanding X involves receiving something (perhaps a form) that represents X. To understand a universal, I don't have to receive the universal itself into my mind (whatever that might mean). Rather, I have to receive a (non-universal, particular) mental impression that's "directed at" or "about" the universal.

But that's my own view. If we accept Aquinas's premises, then his conclusion does follow.

3) A simpler argument for rejecting spiritual matter

I've come up with a much simpler argument for rejecting spiritual matter.

The argument relies on the following idea: the whole reason for supposing that X has matter is to explain (1) X's ability to change into something other than X and/or (2) the ability of something other than X to change into X. We see a bronze cube change into a bronze sphere. Thus, we conclude that there must be something that was first a bronze cube and then a bronze sphere. This something must be potentially a bronze cube and potentially a bronze sphere. In other words, it must be matter for both a bronze cube and a bronze sphere. But if we never saw a bronze sphere change into anything else, and we never saw anything else change into it, then we would have no reason to think that a bronze cube has matter.

With that in mind, the argument is as follows:

1. The only reason for supposing that X has matter is to explain either X's ability to change into something other than X or the ability of something other than X to change into X.
2. A spiritual being doesn't change into anything else (it's immortal and lasts forever), and nothing changes into it (it's created ex nihilo, not formed from some other, previous entity).
3. Therefore, there's no reason for supposing that a spiritual being has matter.

Does anyone know whether Aquinas gives such an argument anywhere?

4) References

Keck, D., 1998. Angels and Angelology in the Middle Ages. Oxford: Oxford UP.

Magee, J., 1999. "Saint Thomas Aquinas and Angels". Thomistic Philosophy Page. Accessed April 13, 2011. Available at: <http://www.aquinasonline.com/Topics/angels.html>.

Maurer, A., 1968. Introduction. Thomas Aquinas. On Being and Essence. Trans. Armand Maurer. Toronto: Pontifical Institute of Medieval Studies.

Spade, P.V., 2008. "Binarium Famosissimum". The Stanford Encyclopedia of Philosophy. Ed. Edward N. Zalta. Available at: <http://plato.stanford.edu/archives/fall2008/entries/binarium/>. [Accessed 14 April 2011]

Thomas Aquinas. 2008. The Summa Theologica of St. Thomas Aquinas. Trans. the Fathers of the English Dominican Province. Ed. Kevin Knight. Available at: <http://www.newadvent.org/summa/>. [Accessed April 14, 2011]

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[1] This is a quote from Magee's private website. However, the opinions expressed there probably reflect scholarly views to an extent, since Magee has himself published on Aristotelian philosophy.

[2] I trust that most readers will understand what I mean by the definition; however, I'll explain it more clearly here. Technically, the definition is ambiguous. After all, there's a sense in which a bronze cube has the potential to be a bronze sphere, since we could melt the cube and recast it as a sphere. But Aristotle presumably wouldn't want to say that a bronze sphere's matter is a bronze cube. We can solve this problem with the following (more precise) definition of matter: M is X's matter if and only if M has the potential to be X while remaining M. Bronze has the potential to be a bronze sphere while remaining bronze, whereas a bronze cube can't become a bronze sphere while remaining a bronze cube.

[3] Technically, the copper and tin are also the bronze sphere's matter, since they're potentially a bronze sphere. A bronze sphere has both bronze and copper and tin as its matter. However, we don't need to get hung up on this complication.

[4] Human beings, in contrast, have an intellectual part—the soul—and a non-intellectual part—the body. However, the soul is united to the body as its form (see my earlier post on hylemorphic dualism).