Augustine doubts our human capacity to fully understand nature. He treats nature's usual, observed course as the surface outcome of the operation of somewhat hidden causal powers in things; a consistent, uniform surface is no more than a prima facie indication of consistent underlying causal powers, and does not reliably reveal these powers, in the grasping of which a proper understanding of nature consists. Events which cause surprise and wonder in us by their apparent extraordinariness by comparison with nature's normal course, may yet, for all we can say, occur by the normal causal powers of the things involved; still these are the events which, particularly when they compel our minds upwards to God, we call miracles. Of course, some events are apparently so beyond the powers of nature that there will be no room for serious doubt that they exceed the casual powers implanted in things.

Aquinas follows Augustine on the miraculous in many ways, but while he retains being wonderful as part of his conception, he distinguishes between the wonder which derives from ignorance of the causes at work in nature and what is wondrous in an unqualified way because it truly has no natural cause. An example of the former sort of wonder will be the person who is amazed by an eclipse of the sun whereas the astronomer, who knows its cause, is not. The name ‘miracle’ suggests ‘what is of itself filled with admirable wonder, not simply in relation to one person or another’.