Many religions throughout history have had a doctrine concerning something like angels and demons. Although the beliefs vary depending on the specific religion, the essential idea is the same. Catholic Church teaching holds that there are literal angels and literal demons. This possibility can be shown through reason but the actual existence of angels and demons is only known by faith (i.e. it has been revealed by God as is clear from both the Old and New Testament writings).
Angels and demons are greatly misunderstood though by contemporaries because of the connotation they have. On a purely intellectual level, they are often dismissed as “superstitious” or “medieval.” Since they are such a strong part of Christian tradition, we have kept them however in a modified form. For instance, a lot of people say that anybody who has died is “now an angel in heaven.” Demons on the other hand are either totally dismissed or thought of as “the force for evil” or just any paranormal phenomena. Who hasn’t heard the scholastic theology derided with the old phrase “that’s like debating how many angels can dance on the head of a pin”?** In any case, I think it’s important to clear up what angels are in order to demonstrate that they (and the rest of scholastic theology in general) are not just the thoughts of crazy inquisition-running prelates but actually intelligible concepts.
So in order to understand angels, we have to understand rationality. We directly experience our own knowledge and free will and indirectly experience the knowledge and free will of other people. Here, knowledge is used to mean intellectual knowledge, otherwise called “understanding.” When one understands, he grasps the intelligibility of a certain type of thing. Take a tree for instance. The intelligibility of a tree is the ‘information’ so to speak which makes a tree a tree. Leaving aside whether or not there is a such thing as a formal cause (or essence) in the natural world, it is clear that a tree is a certain type of thing that acts in a certain way (it is possible to hold a reductionist view where a tree is “nothing more” than the atoms which make it up however this doesn’t eliminate intelligibility, a topic for another time). If the tree were not intelligible, it couldn’t be a certain type of thing with certain distinct behaviors (behavior as understood in a very broad sense). Now, a tree has its intelligibility inherent to it, as that is what makes it a tree. A complete description of the tree necessarily reaches outside of the tree to the very nature of physical reality, but that is beside the point. All that shows is that a tree has limited intelligibility in itself. As people, we can understand a tree. This means that we can grasp the intelligible nature of a tree as well as its relation and dependence on the intelligible nature of physical reality itself. As humans, we are not limited however to understanding a particular tree, or even trees themselves. We can understand many things. This is because we can have in our minds the intelligibility of many different things even though our minds are not identical with those things. This incidentally is a starting point for demonstrating that intellectual activity is immaterial.
In any case, to understand means to grasp what makes something the type of thing it is, to grasp its intelligibility which accounts for the way it acts and why it acts that way. As humans, we begin our understanding with sense experience where we first perceive a particular thing (like a tree) through one of our five senses. We then form a picture of this particular thing in our imagination and from there can begin to understand. Free will then is when we desire what we understand to be good. The will is free because there are many goods of which we are free to choose from. The will always pursues some good. An act is evil when the good which the person chooses is contrary to the person’s good as a whole and thus contrary to reason. Free will is necessarily immaterial in essence as well because matter does not chose. Matter always operates according to the physical principles which guide its nature (physical laws). To act freely is to act not by chance or by laws, it is to act by choice.
An intelligent, or rational being is one that has understanding and free will. God is the very act of understanding and in His understanding He necessarily wills the good according to what is rational (although there are many goods which are truly rational and thus God is free to choose among them). God, being infinite rationality is more than a person. God is what defines being a rational agent, the standard against which other things are set. God is the pure spiritual act of understanding and thus we are only imitations of it and we only participate in a limited fashion in what God has essentially and infinitely. We can do this because of our immaterial souls. Some people think of any mention of an immaterial soul as something “magical” or “supernatural.” Magical is not supernatural however both are incorrect views. The soul is not magical because it is a reasonable belief not a superstition, it does not involve any illusion, and doesn’t involve incantations or anything like that. The soul is not supernatural because by very definition it is part of our natures as human and thus not above the natural. It is true that the soul is above the physical nature of the body, but that doesn’t mean it’s above our nature as human beings. In fact, it is in virtue of the soul that we are human beings rather than merely very complex and advanced animals.
Since understanding and free will are essentially immaterial, it is at least plausible that these activities exist apart from a material body. In humans, this is a little complex because all of our activity that we can experience is directly related to our human bodies, specifically our brain states. However, leaving humans aside, rationality itself is clearly distinct from a material operation and therefore we can at least posit the possibility of non-material intelligences that have never been or never will be related to a physical body. This is what we mean by an angel. From the standpoint of philosophy, what we can show is that since rationality is immaterial, it is possible that there are rational agents totally disconnected from any corporal entity. From the standpoint of theology, we know by revelation that these beings do exist and they are called Angels.
Angels then are just immaterial, rational beings with understanding and will. Since they are not bound to any bit of matter, theologians generally have agreed that angels are (1) more numerous than humans by a significant amount, (2) more intelligent and (3) more powerful. The tradition of the Church teaches that we each have a guardian angel as well. Christian and Jewish history involves God delivering messages through the angels who at times take on a physical appearance in order to communicate with man (as seems to be the case with the Angel Gabriel at the Annunciation for example).
What then is a demon? A demon or devil is just an angel which disobeyed God. Since angels have free will, they have the opportunity to reject God. The tradition holds (again, this is something which we cannot know by reason alone but need God to reveal it to us) that some of the angels disobeyed God and ended up in hell. Now hell may seem like a superstitious idea too, but that is philosophically and theologically defensible as well. Hell, since angels and demons lack physical bodies, is just the state of being separated from God for all of eternity. Theologians generally consider the suffering of the demons in hell to be worse than for humans. There are two reasons. First of all, humans often sin through weakness because of original sin. Angels didn’t have original sin and thus they can only sin through malice. Second, since angels are immaterial, they have better understanding of the evil of their actions. Hence, an evil angel is far more evil than an evil human. Demons consequently suffer worse in hell as they are more distant from God.
What should we think then of all of the depictions and images of angels and demons throughout history? The dragons and the girls with wings? What about the red guy with a pitchfork? What about the babies playing the harp in heaven? All of that kind of thing ranges from a nice artistic representation at best to a misleading misrepresentation at worse. Angels and demons are simply intelligent beings without bodies (and humans who have died although they don’t at the time of death have a body, they were once associated with a body and will be again at the general resurrection according to Catholic belief). Angels are the good ones and demons are the bad ones. Angels are in heaven, praising God and praying for us. They can help us on earth. Demons are in hell and attempt to tempt us on earth. When we speak of spiritual warfare we don’t mean angels and demons having a physical war with St. Michael literally kicking Satan out of heaven. We mean that angels and demons are battling for our souls. The devil hates man and hates God, the angels want to help us.
Some of this may sound a little fantastic to the modern mind. At this is understandable since most of us haven’t encountered an angel or a demon. If we did, we would probably be very shocked. Even Mary was shocked when confronted with Gabriel (as the Angel told her to “fear not”). Yet still, once we understand that intelligence and free will can exist apart from a body, it should just seem like a reasonable possibility that angels exist. Since Christ talks about the existence of angels and demons, it is only rational to believe that they do in fact exist.
** http://newadvent.org/summa/1052.htm#article3 This is the article where Aquinas specifically discusses the “location” of angels. He doesn’t ask about dancing on the head of a pin, but he does ask if more than one angel can be in the same place at the same time. As should be clear from his discussion on angels, he doesn’t think that they are physical. Therefore, to be in a place for an angel means to be causally effecting the location. From here Aquinas reasons that there cannot be two angels present. Regardless of whether or not he is correct, he is asking an intelligent question and gives intelligent reasons to back it up.