Since the rank of the angels is determined by nature and grace, it follows that, as regards nature, the demons are still in their Orders; for their natural gifts are not taken from them; while as regards grace their state is twofold; for there is the state of perfect grace, or Glory, in which they have never been; and that of imperfect grace, in which they were once associated with the angels, and from which they have fallen.
And there is prelacy among them; for, since the Divine Wisdom leaves nothing without order, their actions are subordinated, and prelacy signifies that the action of inferiors is subject to that of superiors, as natural order signifies that the lower natures are ordered to the higher ones. And as particular faculties are governed by universal ones, so corporeal natures are governed by spiritual ones, which, being nearer to God and more perfect, have influence over others: therefore, as the demons are deprived of this perfection, it follows that the good angels have prelacy over them and govern them.
Neither can one demon illuminate another, because through perversity they are averted from God; they can, however, intimate their thoughts to each other by mode of speech.
- text taken from Compendium of the Summa Theologica of Saint Thomas Aquinas, by Bishop Berardus Bongiovanni