Objection 1. It would seem that the orders of the angels are not properly named. For all the heavenly spirits are called angels and heavenly virtues. But common names should not be appropriated to individuals. Therefore the orders of the angels and virtues are ineptly named.
Objection 2. Further, it belongs to God alone to be Lord, according to the words, "Know ye that the Lord He is God" (Psalm 99:3). Therefore one order of the heavenly spirits is not properly called "Dominations."
Objection 3. Further, the name "Domination" seems to imply government and likewise the names "Principalities" and "Powers." Therefore these three names do not seem to be properly applied to three orders.
Objection 4. Further, archangels are as it were angel princes. Therefore this name ought not to be given to any other order than to the "Principalities."
Objection 5. Further, the name "Seraphim" is derived from ardor, which pertains to charity; and the name "Cherubim" from knowledge. But charity and knowledge are gifts common to all the angels. Therefore they ought not to be names of any particular orders.
Objection 6. Further, Thrones are seats. But from the fact that God knows and loves the rational creature He is said to sit within it. Therefore there ought not to be any order of "Thrones" besides the "Cherubim" and "Seraphim." Therefore it appears that the orders of angels are not properly styled.
On the contrary is the authority of Holy Scripture wherein they are so named. For the name "Seraphim" is found in Isaiah 6:2; the name "Cherubim" in Ezekiel 1 (Cf. 10:15-20); "Thrones" in Colossians 1:16; "Dominations," "Virtues," "Powers," and "Principalities" are mentioned in Ephesians 1:21; the name "Archangels" in the canonical epistle of St. Jude (9), and the name "Angels" is found in many places of Scripture.
I answer that, As Dionysius says (Coel. Hier. vii), in the names of the angelic orders it is necessary to observe that the proper name of each order expresses its property. Now to see what is the property of each order, we must consider that in coordinated things, something may be found in a threefold manner: by way of property, by way of excess, and by way of participation. A thing is said to be in another by way of property, if it is adequate and proportionate to its nature: by excess when an attribute is less than that to which it is attributed, but is possessed thereby in an eminent manner, as we have stated (13, 2) concerning all the names which are attributed to God: by participation, when an attribute is possessed by something not fully but partially; thus holy men are called gods by participation. Therefore, if anything is to be called by a name designating its property, it ought not to be named from what it participates imperfectly, nor from that which it possesses in excess, but from that which is adequate thereto; as, for instance, when we wish properly to name a man, we should call him a "rational substance," but not an "intellectual substance," which latter is the proper name of an angel; because simple intelligence belongs to an angel as a property, and to man by participation; nor do we call him a "sensible substance," which is the proper name of a brute; because sense is less than the property of a man, and belongs to man in a more excellent way than to other animals.
So we must consider that in the angelic orders all spiritual perfections are common to all the angels, and that they are all more excellently in the superior than in the inferior angels. Further, as in these perfections there are grades, the superior perfection belongs to the superior order as its property, whereas it belongs to the inferior by participation; and conversely the inferior perfection belongs to the inferior order as its property, and to the superior by way of excess; and thus the superior order is denominated from the superior perfection.
So in this way Dionysius (Coel. Hier. vii) explains the names of the orders accordingly as they befit the spiritual perfections they signify. Gregory, on the other hand, in expounding these names (Hom. xxxiv in Evang.) seems to regard more the exterior ministrations; for he says that "angels are so called as announcing the least things; and the archangels in the greatest; by the virtues miracles are wrought; by the powers hostile powers are repulsed; and the principalities preside over the good spirits themselves."
Reply to Objection 1. Angel means "messenger." So all the heavenly spirits, so far as they make known Divine things, are called "angels." But the superior angels enjoy a certain excellence, as regards this manifestation, from which the superior orders are denominated. The lowest order of angels possess no excellence above the common manifestation; and therefore it is denominated from manifestation only; and thus the common name remains as it were proper to the lowest order, as Dionysius says (Coel. Hier. v). Or we may say that the lowest order can be specially called the order of "angels," forasmuch as they announce things to us immediately. "Virtue" can be taken in two ways.
First, commonly, considered as the medium between the essence and the operation, and in that sense all the heavenly spirits are called heavenly virtues, as also "heavenly essences."
Secondly, as meaning a certain excellence of strength; and thus it is the proper name of an angelic order. Hence Dionysius says (Coel. Hier. viii) that the "name 'virtues' signifies a certain virile and immovable strength"; first, in regard of those Divine operations which befit them; secondly, in regard to receiving Divine gifts. Thus it signifies that they undertake fearlessly the Divine behests appointed to them; and this seems to imply strength of mind.
Reply to Objection 2. As Dionysius says (Div. Nom. xii): "Dominion is attributed to God in a special manner, by way of excess: but the Divine word gives the more illustrious heavenly princes the name of Lord by participation, through whom the inferior angels receive the Divine gifts." Hence Dionysius also states (Coel. Hier. viii) that the name "Domination" means first "a certain liberty, free from servile condition and common subjection, such as that of plebeians, and from tyrannical oppression," endured sometimes even by the great.
Secondly, it signifies "a certain rigid and inflexible supremacy which does not bend to any servile act, or to the act, of those who are subject to or oppressed by tyrants."
Thirdly, it signifies "the desire and participation of the true dominion which belongs to God." Likewise the name of each order signifies the participation of what belongs to God; as the name "Virtues" signifies the participation of the Divine virtue; and the same principle applies to the rest.
Reply to Objection 3. The names "Domination," "Power," and "Principality" belong to government in different ways. The place of a lord is only to prescribe what is to be done. So Gregory says (Hom. xxiv in Evang.), that "some companies of the angels, because others are subject to obedience to them, are called dominations." The name "Power" points out a kind of order, according to what the Apostle says, "He that resisteth the power, resisteth the ordination of God" (Romans 13:2). And so Dionysius says (Coel. Hier. viii) that the name "Power" signifies a kind of ordination both as regards the reception of Divine things, and as regards the Divine actions performed by superiors towards inferiors by leading them to things above. Therefore, to the order of "Powers" it belongs to regulate what is to be done by those who are subject to them. To preside [principari] as Gregory says (Hom. xxiv in Ev.) is "to be first among others," as being first in carrying out what is ordered to be done. And so Dionysius says (Coel. Hier. ix) that the name of "Principalities" signifies "one who leads in a sacred order." For those who lead others, being first among them, are properly called "princes," according to the words, "Princes went before joined with singers" (Psalm 67:26).
Reply to Objection 4. The "Archangels," according to Dionysius (Coel. Hier. ix), are between the "Principalities" and the "Angels." A medium compared to one extreme seems like the other, as participating in the nature of both extremes; thus tepid seems cold compared to hot, and hot compared to cold. So the "Archangels" are called the "angel princes"; forasmuch as they are princes as regards the "Angels," and angels as regards the Principalities. But according to Gregory (Hom. xxiv in Ev.) they are called "Archangels," because they preside over the one order of the "Angels"; as it were, announcing greater things: and the "Principalities" are so called as presiding over all the heavenly "Virtues" who fulfil the Divine commands.
Reply to Objection 5. The name "Seraphim" does not come from charity only, but from the excess of charity, expressed by the word ardor or fire. Hence Dionysius (Coel. Hier. vii) expounds the name "Seraphim" according to the properties of fire, containing an excess of heat. Now in fire we may consider three things.
First, the movement which is upwards and continuous. This signifies that they are borne inflexibly towards God.
Secondly, the active force which is "heat," which is not found in fire simply, but exists with a certain sharpness, as being of most penetrating action, and reaching even to the smallest things, and as it were, with superabundant fervor; whereby is signified the action of these angels, exercised powerfully upon those who are subject to them, rousing them to a like fervor, and cleansing them wholly by their heat.
Thirdly we consider in fire the quality of clarity, or brightness; which signifies that these angels have in themselves an inextinguishable light, and that they also perfectly enlighten others.
In the same way the name "Cherubim" comes from a certain excess of knowledge; hence it is interpreted "fulness of knowledge," which Dionysius (Coel. Hier. vii) expounds in regard to four things: the perfect vision of God; the full reception of the Divine Light; their contemplation in God of the beauty of the Divine order; and in regard to the fact that possessing this knowledge fully, they pour it forth copiously upon others.
Reply to Objection 6. The order of the "Thrones" excels the inferior orders as having an immediate knowledge of the types of the Divine works; whereas the "Cherubim" have the excellence of knowledge and the "Seraphim" the excellence of ardor. And although these two excellent attributes include the third, yet the gift belonging to the "Thrones" does not include the other two; and so the order of the "Thrones" is distinguished from the orders of the "Cherubim" and the "Seraphim." For it is a common rule in all things that the excellence of the inferior is contained in the superior, but not conversely. But Dionysius (Coel. Hier. vii) explains the name "Thrones" by its relation to material seats, in which we may consider four things.
First, the site; because seats are raised above the earth, and to the angels who are called "Thrones" are raised up to the immediate knowledge of the types of things in God.
Secondly, because in material seats is displayed strength, forasmuch as a person sits firmly on them. But here the reverse is the case; for the angels themselves are made firm by God.
Thirdly, because the seat receives him who sits thereon, and he can be carried thereupon; and so the angels receive God in themselves, and in a certain way bear Him to the inferior creatures.
Fourthly, because in its shape, a seat is open on one side to receive the sitter; and thus are the angels promptly open to receive God and to serve Him.
Source: Summa Theologica (New Advent)