‘It is not only Christians, Jews and Muslims who believe in angels. Pagans have believed in them as well. Aristotle, for example, argued that there are immaterial beings responsible for the motion of the heavens (see Metaphysics 12:8), and Plotinus said that there are “guardian spirits” (see Enneads 3:4). Why has it seemed to so many, whatever their religious convictions (or lack of them), that the class of intelligent beings is not exhausted by us humans: that there ought to exist intelligences “other” and “higher” than our own? Benedict Ashley has provided an impressive answer:

‘It is uncomfortable to the modern mind to suppose that we human beings are the only intelligences in the universe. To understand this discomfort, which has resulted in the proliferation of science fiction fantasies about life in other worlds and in perfectly serious efforts of scientists to communicate with other humanoids, we should note that one of the modes of creative thinking that has paid off richly in science, although of course it always requires testing against the evidence, is extrapolation or pattern thinking. For example, Mendeleev’s periodic table was based on symmetrical arrangement of known elements according to their properties, but it contained blanks. Eventually it was possible to fill in these blanks by the discovery of new elements. Again, the table of possible kinds of crystalline structures was first worked out mathematically from known types and the blanks were eventually all filled in by new discoveries. Our evolutionary view of the world presents us with a great variety of kinds of primary units from atoms to the most complex of living forms. We are always looking for “missing links” to complete this pattern. Whenever we find a new type of living thing we immediately suspect that we will soon discover that it has “radiated” in a number of genera and species adapted to the various possible environmental niches.

‘Therefore, when we discover that in our visible universe there is a type of organism, the human species, which introduces a wholly new principle of behavior, namely abstract, symbolically expressed, creative thought, we naturally conjecture that the very limited exemplification of this type of life found only in the single human species cannot be the only one. If we also accept that the world has been created by a God who is an infinite intelligence, we are even more struck by the immense gap that lies between these two extremes of mental power, the human and the divine. Undoubtedly this gap must still puzzle us today, just as it puzzled ancient people the world over, and even more so because we have greater awareness both of the wonderful scale of natural forms and of the vast differences between the human beings who have attained to scientific understanding and technological control of the world and the other animals.’

(Kreeft & Tacelli, Handbook of Apologetics, citing Theologies of the Body, Mt. 13)