Revelation Concerning the Angels of Christian Angelology
FROM THE FUNDAMENTALS OF CATHOLIC DOGMA
Ludwig Ott

§ 26. Existence, Origin and Number of Angels

2. Number of the Angels

The number of the Angels is, according to Holy Writ, very great. The Scriptures speak of myriads [Heb. 12:22] of thousands and thousands [Dan. 7:10; Apoc. 5:11], of legions [Matt. 26:22]. The various biblical names indicate a gradation and order among the Angels. Since the time of Pseudo-Dionysius,  nine Choirs or Orders of Angels are named of which each three form a hierarchy. In accordance with Holy Scripture these are called: Seraphim, Cherubim, Thrones, Principalities, Powers, Strengths [Virtues], Highnesses [Dominations], Archangels, and Angels. Cf. Is. 6:2 et seq., Gen. 3: 24; Col. 1:16; Eph. 1:21; 3:10; Rom. 8:38 et seq.; Jud. 9; 1 Thess. 4:16.

The division of the Angel-world into nine Orders and the illumination of the lower Orders through the higher Orders---a teaching which stems from neo-Platonism---is not a truth of Faith, but a free theological opinion. The same applies to the grouping of Angels by the Schoolmen, which goes back to Dan. 7:10, into angeli assistentes and angel ministrantes [assistants at the Throne---messengers of God]. To the former group are allocated the upper six choirs, to the latter group the lower three. Revelation testifies however that the functions of assisting and serving are not mutually exclusive. Cf. Tob. 12:15; Luke 1:19, 26.

According to the teaching of St. Thomas, which is connected with the doctrine of the principle of individuation, the Angels are specifically distinguished from one another; thus each Angel forms a separate species. Other theologians, as against this, teach either that all the Angels together form one species only [St. Albert the Great] of that the individual hierarchies or choirs form particular species [the Franciscan school, Suarez].