Swinburne’s description of Aquinas’ concept of a ‘miracle’:

Aquinas wrote that a ‘miracle’ in a wide sense is any event brought about by a rational agent in virtue of powers greater than normal human powers; and so many events brought about by demons or angels would count as miracles. But in a strict sense, he claims, a miracle is that which occurs outside the whole system of created nature; it is that which no other agent except God has the power to bring about. See Summa Theologiae, Ia.114. (Existence of God, 2nd ed., from footnote on p.282)

3. ‘occurs outside the whole system of created nature’

This is a neccessary condition of the ‘strict sense’ of the word ‘miracle’.

The words describing this condition are unclear, even misleading. Any event involving physical objects or human beings would seem to occur inside the ‘system of created nature’ (assuming that nature was created by someone), so taking this description literally would result in ruling out just about every alleged miracle in the Bible.

The parting of the Red Sea involved the movement of physical water (if the event really happened), and that water was part of the ‘system of created nature’ (assuming that nature was created by someone), so that would be ruled out as not being a miracle. Jesus’ walking on water or turning water into wine also involved changes to physical water, which is part of the ‘system of created nature’, so those events would also be ruled out as not being miracles, it would seem.

The phrase ‘created nature’ is intended to point to a distinction between created things and God, who has always existed and who is not a created being. By limiting the scope of ‘miracle’ to events outside of ‘the whole system of created nature’, Aquinas is trying to exclude events caused by spirits other than God (e.g. by angels and demons).

On the Christian worldview there are supernatural beings who were created by God (e.g. angels and demons) and given certain supernatural powers by God. If such a being intervenes in the natural world (e.g. a demon possesses the body of some human being, or an angel causes a car to veer to the right to avoid a collision), that is a ‘supernatural’ event caused by a ‘supernatural’ being, but it is also an event caused by a creature with a created nature who is simply performing actions that God gave it the power to perform.

The nature of an angel (or a demon) allows it to do things that may contravene some laws of physics, but that is, in a sense, only natural for an angel (or demon), because God created angels and demons to have such power over (at least some) laws of physics. So, the possession of a human by a demonic spirit or the veering of a car caused by an angel can be viewed as events that occur inside ‘the whole system of created nature’ even though this would be a supernatural event in the sense that it involves the suspension or violation of a law of physics. The ‘whole system’ thus includes supernatural (i.e. bodiless, non-physical) beings and their powers and activities.

Only God and his actions, are outside of the ‘whole system of created nature’. But if God intervenes in ordinary physical events (e.g. the flow and position of water in the Red Sea), then God and his actions may be outside of the ‘whole system of created nature’ but the effects of this activity are still in and upon objects and events inside the ‘whole system of created nature’. (This seems analogous to the mind/body problems of dualism.)

Can we re-state the condition in a clearer way that avoids the confusion that I have pointed out? The point seems to be to isolate certain events that are such that “no other agent except God has the power to bring about”. But no such events exist, because God can grant to whomever he wishes whatever power he wishes to grant that person. If God wants to give Moses the power to part the Red Sea, then God can give that power to Moses, even though this is not a normal power for human beings to possess. So, I don’t see how this strategy can possibly work.

It seems much simpler to just add the condition that it must be God who brings about the event. This would straightforwardly eliminate events brought about by angels and demons from the scope of the word ‘miracle’.