Question Two of Chapter One of the Third Decade
What demons are
It is asked what those beings which we call demons are.
To this Augustine responds upon Genesis, reporting the opinion of the Platonists; and it is set down in the Decretum, chapter Sciendum, cause 26, question 3.
He describes evil angels thus: “Demons are animals in genus, most beautiful in nature, rational in mind, passive in soul, aerial in body, and eternal in duration.”
He says in genus, namely in the genus of nature and the predicamental category of substance.
They are most beautiful in nature, for with respect to the substance of their nature they are not more base than the good angels.
They are passive in soul, with passions, according to the Platonists, of the appetites of sensuality, namely the concupiscible and the irascible.
They are aerial in body insofar as they were created from subtler matter, as the Gloss upon the Decretum says in the place cited above, so that it may be understood that they understand more subtly and swiftly than human beings.
They are eternal in duration, namely through grace and not through nature.
Likewise Augustine in The City of God also describes them thus: “Demons are spirits most greedy to harm, altogether alien from justice, swollen with pride, livid with envy, and crafty in deceit. They indeed inhabit this air because, cast down from the sublimity of the higher heaven, they have by merit been condemned irreversibly in a place fitting to them as in a prison.”
And evil angels are called diaboli, from dia, which is “two,” and bolus, which is “morsel,” as if desiring two morsels, namely those of souls and bodies, as is said in the Ordinary Gloss upon chapter Firmiter, On the Supreme Trinity.
Diabolus is also said in Hebrew as if “flowing downward.” In Greek it is said to mean “accuser”; in Latin, “evil angel,” as Isidore says in Book VIII of the Etymologies.
He is also called Satan, as if “adversary,” and demon, as if one skilled in things.
These things are from the authorities cited above.
Addition
He says: “Demons are animals in genus.”
For Hermes Trismegistus, all the Academics, and many of our more ancient doctors assert that angels are corporeal and animate.
For Saint Basil says: “Angels possess bodies like certain fine, aerial, and pure spirits.”
Certainly an angel could not be moved from place to place unless it possessed a body, since local motion belongs to a body alone.
But as far as the title of the question is concerned, we have from Porphyry and Proclus that there is a twofold genus of evil demons.
For one is the genus of souls or of substantial and intellectual demons; the other, however, is the genus of material powers, such as the animal appetites which always oppose the spirit.
And Michael Psellus, following the thought of Plato, Porphyry, and Proclus, reduces them to four principal genera, namely the earthly, watery, aerial, and fiery.
For the earthly oppose us through the flesh; the watery through blood mixed with phlegm; the aerial through the spirit of pride; and the fiery through inflamed anger.
But take good notice in the chapter cited above that Augustine is reporting the opinion of others rather than stating what he himself thought concerning certain things which are said about spirits.
Such is the statement that they were created from subtler matter, for it is a moral discourse.
They are also eternal by nature a parte post, unless he wishes to say that they are eternal through that general grace by which all things are preserved in being, or through grace in view of their demerits when speaking of demons; for they rendered themselves unworthy of existence.