Angels, as Aquinas and other Scholastic theologians conceive of them, are purely intellectual substances, minds separated from matter. An angel thinks and wills but has no corporeal operations at all. Naturally, then, popular images of angels – creatures with wings, long flowing robes, and so forth – have nothing to do with the real McCoy. For a modern philosopher, the easiest way to understand what an angel is is to conceive of it as a Cartesian res cogitans– though as we will see in what follows, in a way this actually gets things the wrong way around.
You do not have to believe in angels in order to find the notion of philosophical interest. Working out the implications of the idea of a purely incorporeal intellect is useful for understanding the nature of the intellect, the nature of free choice and its relationship to the presence or absence of the body, the nature of time, and other issues too. In fact there is such a thing as rational angelology, and here as elsewhere Aquinas often surprises with his demonstration of how much might be established via purely philosophical arguments.
The position of angels in the hierarchy of reality illuminates the similarities and differences between the kinds of things which exist (or, if you don’t believe in angels, which could exist). At the bottom of the hierarchy come inanimate material things – rocks, dirt, water, and so forth. Next come the vegetative forms of life, which take in nutrients, grow, and reproduce themselves but do nothing beyond this. Then we have sensory or animal forms of life, which carry out the vegetative functions but add to them sensation, appetite, and locomotion or self-movement. Above mere animals are rational animals or human beings. Human beings do everything other animals do, but on top of that possess intellect and will; and for Aquinas and other Scholastic thinkers, these are incorporeal activities. A human being is, accordingly, the kind of substance which possesses at the same time both bodily and non-bodily attributes.
Now, there is, as it were, metaphysical room in between human beings and God for a further kind of thing – something which is entirelyincorporeal rather than being merely partially incorporeal (as human beings are), but which is nevertheless finite and in need of being created (as God is not). That is what an angel is.
On Aquinas’s analysis, among the things we can say about angels are the following:
1. Being utterly incorporeal by nature, angels lack sense organs or brain activity. They do not have sensory experiences, or the mental imagery that follows upon these. Hence their mode of knowledge is not like ours. We come to know things through the senses, and form concepts by abstracting them from the things we experience. An angel, by contrast, has all its concepts and knowledge “built in” at its creation. In other words, it possesses innate ideas.
2. Angels are not in time, though they are not strictly eternal either. What is in time, as corporeal things are, is changeable both in its substance and in its accidents. What is strictly eternal, as God is, is utterly unchangeable. Angels are unchangeable in their substance, since they are incorporeal. An angel is not composed of matter which might lose its substantial form and thereby go out of existence. It is in this way incorruptible or immortal. But it can change in its accidents insofar as it can choose either this or that. This middle ground between time and eternity is what Aquinas calls “aeviternity.”
3. For these reasons, an angel does not know things in a discursive way. It does not have to engage in processes like reasoning from premises to a conclusion, weighing alternative hypotheses, or otherwise “figuring things out” the way we do. It simply knows what it knows “all at once,” as it were.
4. Unlike the human soul, an angel is not the form of any body. A human being, again, is the kind of substance which possesses both corporeal and incorporeal activities. It accordingly has the substantial form of the kind of thing capable of both activities. When its corporeal side is destroyed, the substance itself is not thereby destroyed, because it was never entirely corporeal in the first place. That is why the human soul carries on beyond death – qua substantial form, it continues to inform the now incomplete substance of which it is the form, a substance reduced to its incorporeal operations. But this is not its natural state. In the absence of matter, the substance in question cannot do all the things it is naturally inclined to do (seeing, hearing, walking, talking, etc.). But angels are not like that. Being incorporeal is their natural state.
5. All angels fall under the same genus (which is why they are all angels), but there cannot be more than one member of any angelic species. The reason is that, for Aquinas, matter is what distinguishes one member of a species of thing from another. Hence, since angels are completely incorporeal, there is no way in principle by which one member of an angelic species could be distinguished from another. If there are two or more angels, then, there are ipso facto two or more angelic species. The way these species differ is the only way they can differ in purely intellectual substances, viz. degree of intellectual power.
See (among other works) Summa TheologiaeI.50-64 for more details. But this much gives us enough to understand why, from an Aristotelian-Thomistic point of view, the Cartesian view of human nature is deeply mistaken. To be sure, like the Cartesian, the Aristotelian-Thomistic philosopher regards the human intellect as incorporeal. But that does not suffice to make for a purely incorporeal substance. Rather, a human being is a substance which of its nature possesses both corporeal and incorporeal operations.
A Cartesian res cogitans, by contrast, is a thing that thinks and nothing more than that. That is why the Cartesian (unlike the Aristotelian-Thomistic philosopher) is a substance dualist. The res cogitans is an utterly incorporeal substance but nevertheless a complete one. The body must accordingly be a second, distinct complete substance. From an Aristotelian-Thomistic point of view, this entails that with Descartes’ res cogitans, we are no longer talking about a human intellect at all. We are really implicitly talking about an angelicintellect. (This was not Descartes’ own intention, to be sure. The point, though, is that that is what his position entails, whether he welcomes it or not.)
As I noted in another post not too long ago, the famous mind-body interaction problem facing the Cartesian ultimately is not, from the Aristotelian-Thomistic point of view, the problem of explaining how an incorporeal substance can be the efficient cause of a bodily event. After all, God causes the physical world to exist, and angels can cause various events in the natural world to occur, and these cases do not raise any special problem about causation. (Or at least, Aristotelian-Thomistic philosophers don’t think these cases any more problematic than Cartesians do.)
The problem facing the Cartesian is rather how to explain mind-body interaction in a way that doesn’t reduce it to something comparable to demonic possession. A fallen angel moves a bit of matter around in something like the way a poltergeist is popularly thought to move material things around. A Cartesian res cogitans controlling a res extensa is essentially like a demon’s control of one of the Gadarene swine – the manipulation of something utterly extrinsic to the manipulator, to which it is only contingently related. That is a bizarre model of human nature that is not compatible with the intimate way we are actually related to our own bodies, which is why Gilbert Ryle famously characterized the Cartesian view as the theory of the “ghost in the machine.”
The fact that Descartes attributes innate ideas to us only underlines the extent to which his model of human nature is essentially an angelic model. And if Aquinas’s analysis of the angelic nature is correct, it entails further arguments against the Cartesian view of human nature. If the Cartesian view were correct, then (since it entails that the human intellect is essentially angel-like), it would follow that human knowledge would be “all at once” rather than discursive, that human intellects would not exist in time, and that each human being would be the unique member of his own species. But none of these things is true. Hence the Cartesian view of human nature is not correct.
Of course, Cartesians do not in fact attribute all of these features to a res cogitans, which is why it is not a perfect model for what an angelic intellect is like. The Cartesian does not see the implications of severing the human intellect from the body as thoroughly as Descartes severs it. Strictly speaking, the proper procedure is not to try to understand angels in terms of res cogitans, but rather to understand the notion of res cogitans– including the implicit aspects that Cartesians do not see – in light of the Thomistic analysis of angelic intellects.
