Go [Vulg. 'Depart from Me'], you cursed, into everlasting fire, which
was prepared for the devil and his angels" (Matt. 25:41). For the order
of Divine justice exacts that whosoever consents to another's evil
suggestion, shall be subjected to him in his punishment; according to
(2 Pet. 2:19): "By whom a man is overcome, of the same also he is the
slave."

Reply Obj. 1: Although the demons all sinned in the one instant, yet
the sin of one could be the cause of the rest sinning. For the angel
needs no delay of time for choice, exhortation, or consent, as man,
who requires deliberation in order to choose and consent, and vocal
speech in order to exhort; both of which are the work of time. And it
is evident that even man begins to speak in the very instant when he
takes thought; and in the last instant of speech, another who catches
his meaning can assent to what is said; as is especially evident with
regard to primary concepts, "which everyone accepts directly they are
heard" [*Boethius, De Hebdom.].

Taking away, then, the time for speech and deliberation which is
required in us; in the same instant in which the highest angel
expressed his affection by intelligible speech, it was possible for
the others to consent thereto.

Reply Obj. 2: Other things being equal, the proud would rather be
subject to a superior than to an inferior. Yet he chooses rather to
be subject to an inferior than to a superior, if he can procure an
advantage under an inferior which he cannot under a superior.
Consequently it was not against the demons' pride for them to wish to
serve an inferior by yielding to his rule; for they wanted to have
him as their prince and leader, so that they might attain their
ultimate beatitude of their own natural powers; especially because in
the order of nature they were even then subject to the highest angel.

Reply Obj. 3: As was observed above (Q. 62, A. 6), an angel has
nothing in him to retard his action, and with his whole might he is
moved to whatsoever he is moved, be it good or bad. Consequently
since the highest angel had greater natural energy than the lower
angels, he fell into sin with intenser energy, and therefore he
became the greater in malice.
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NINTH ARTICLE [I, Q. 63, Art. 9]

Whether Those Who Sinned Were As Many As Those Who Remained Firm?

Objection 1: It would seem that more angels sinned than stood firm.
For, as the Philosopher says (Ethic. ii, 6): "Evil is in