By definition, a miracle is a work which transcends the powers of nature, where by 'nature' is understood the physical forces, material and mental, of which we have ordinary experience in this life. Beyond the world in which we live there is the world of spirits, -- of disembodied human souls, of angels, good and bad, and of God. Whatever any power of nature does of itself is, by definition, excluded from the category of the miraculous. But a question arises whether, if disembodied spirits or angels, good or bad, ever effect any sensible change in this world of matter and sense, such a change should be called a miracle. To that question St Thomas addresses himself in the succeeding chapter.
Of God and His Creatures: 3.102