Objection 1. It would seem that the angels can work miracles. For Gregory says (Hom. xxxiv in Evang.): "Those spirits are called virtues by whom signs and miracles are usually done."
Objection 2. Further, Augustine says (QQ. 83, qu. 79) that "magicians work miracles by private contracts; good Christians by public justice, bad Christians by the signs of public justice." But magicians work miracles because they are "heard by the demons," as he says elsewhere in the same work [Cf. Liber xxi, Sentent., sent. 4: among the supposititious works of St. Augustine]. Therefore the demons can work miracles. Therefore much more can the good angels.
Objection 3. Further, Augustine says in the same work [Cf. Liber xxi, Sentent., sent. 4: among the supposititious works of St. Augustine] that "it is not absurd to believe that all the things we see happen may be brought about by the lower powers that dwell in our atmosphere." But when an effect of natural causes is produced outside the order of the natural cause, we call it a miracle, as, for instance, when anyone is cured of a fever without the operation of nature. Therefore the angels and demons can work miracles.
Objection 4. Further, superior power is not subject to the order of an inferior cause. But corporeal nature is inferior to an angel. Therefore an angel can work outside the order of corporeal agents; which is to work miracles.
On the contrary, It is written of God (Psalm 135:4): "Who alone doth great wonders."
I answer that, A miracle properly so called is when something is done outside the order of nature. But it is not enough for a miracle if something is done outside the order of any particular nature; for otherwise anyone would perform a miracle by throwing a stone upwards, as such a thing is outside the order of the stone's nature. So for a miracle is required that it be against the order of the whole created nature. But God alone can do this, because, whatever an angel or any other creature does by its own power, is according to the order of created nature; and thus it is not a miracle. Hence God alone can work miracles.
Reply to Objection 1. Some angels are said to work miracles; either because God works miracles at their request, in the same way as holy men are said to work miracles; or because they exercise a kind of ministry in the miracles which take place; as in collecting the dust in the general resurrection, or by doing something of that kind.
Reply to Objection 2. Properly speaking, as said above, miracles are those things which are done outside the order of the whole created nature. But as we do not know all the power of created nature, it follows that when anything is done outside the order of created nature by a power unknown to us, it is called a miracle as regards ourselves. So when the demons do anything of their own natural power, these things are called "miracles" not in an absolute sense, but in reference to ourselves. In this way the magicians work miracles through the demons; and these are said to be done by "private contracts," forasmuch as every power of the creature, in the universe, may be compared to the power of a private person in a city. Hence when a magician does anything by compact with the devil, this is done as it were by private contract. On the other hand, the Divine justice is in the whole universe as the public law is in the city. Therefore good Christians, so far as they work miracles by Divine justice, are said to work miracles by "public justice": but bad Christians by the "signs of public justice," as by invoking the name of Christ, or by making use of other sacred signs.
Reply to Objection 3. Spiritual powers are able to effect whatever happens in this visible world, by employing corporeal seeds by local movement.
Reply to Objection 4. Although the angels can do something which is outside the order of corporeal nature, yet they cannot do anything outside the whole created order, which is essential to a miracle, as above explained.
Source: Summa Theologica (New Advent)