St. Thomas Aquinas on the Nature and Existence of Angels.

Thomas argues that the fullness of the universe requires the presence of intellectual creatures. Since God wills the good for everything He creates, He also wills that creation resemble Him in some way. And because an effect most closely resembles its cause when it shares the very feature through which it was produced, the created world must contain beings endowed with intellect and will. God creates by knowing and loving, so something in creation must reflect this mode of causation.

For this reason, the perfection of the universe calls for intellectual creatures. Yet understanding cannot be the act of a body or of any bodily power. Therefore, the completeness of creation implies the existence of an incorporeal creature (ST Ia 50, 1).

However, since human beings themselves are intellectual creatures, this alone does not allow us to conclude that there must be purely intellectual beings such as angels. To know that such beings exist, we rely on Sacred Scripture, which speaks clearly about them. Because Scripture affirms their existence, it belongs to Sacred Doctrine to treat angels scientifically. Theology, grounded in faith, has the means to establish both the fact that angels exist and the nature they possess (ST Ia 1, 3). Once their existence is accepted on faith, or even taken hypothetically, philosophical reflection can still uncover many truths about what they must be like. Thomas’s treatment in the Summa provides an excellent model for thinking coherently about the angelic world.

Since angels are intellectual creatures, Thomas concludes that they must be pure spirits, that is, subsistent forms. They are entirely immaterial and possess no bodies of any kind (ST Ia 50, 2). Some thirteenth-century Franciscan theologians, including St. Bonaventure, held the theory of “universal hylomorphism,” according to which everything except God is composed of matter and form. They claimed that angels were made of “spiritual matter.” For Aquinas, this is a contradiction in terms. If something is spiritual, then precisely as spiritual it cannot be material. Even though human beings are both spiritual and bodily, the human soul itself is not composed of spiritual matter and form, contrary to the Franciscan view.

Interestingly, a modern echo of universal hylomorphism appears in certain physicalist theories of mind, especially functionalism. Functionalists such as Hilary Putnam argue that even disembodied spirits would have functional mental states. But for this to be true, such spirits would need to possess parts made of “spiritual matter” capable of interacting functionally, which is exactly the confusion Aquinas rejects.

Angels are not thin, vapor-like material entities, nor are they the souls of the dead. Human souls are naturally ordered to bodies and know through bodily faculties. Angels, by contrast, are pure intellects and are not naturally united to any body (ST Ia 51, 1). Their mode of knowing is almost entirely foreign to ours. This alone is enough to show that angels cannot be identified with separated human souls. Thomas therefore has strong philosophical grounds for rejecting the idea that angels are simply the spirits of deceased relatives.

What may seem surprising is that, despite being wholly immaterial, Thomas maintains that angels sometimes appear in bodily form. Scripture frequently presents angels in a way that allows them to be seen by many people at once. Thomas insists that such appearances must involve bodily vision, and bodily vision requires a physical object. Hence, the bodies seen in these accounts cannot be the angels’ own, since angels have no natural bodies. They must instead be bodies assumed for the occasion (ST Ia 51, 2).

These assumed bodies cannot belong to angels by nature, because intellectual activity cannot depend on a bodily organ (ST Ia 51, 1). If one accepts, on theological grounds, that angels exist and sometimes appear, then it follows that they must shape matter in order to manifest themselves. As Thomas puts it, “by divine power sensible bodies are so fashioned by angels as to fittingly represent the intelligible properties of an angel” (ST Ia 51, 2 ad 2).

To end let us pray to our Guardian Angel;

Angel of God, my guardian dear,
To whom God's love commits me here,
Ever this day [or night], be at my side,
To light and guard, to rule and guide.
Amen.