I've been preparing for a busy next week, so I am behind on almost everything. But for whatever reason there has been talk of miracles in a lot of different places online, and I wanted to put down a few still-inchoate thoughts on the subject, in no particular order.
(1) A miracle is in its proper genus a sign. A sign is something manifesting something to something, or, to speak more precisely, using the terminology of C. S. Peirce, a representamen (R), an object (O), and an interpretant (I) in triadic relation. For the miracle to function as a sign, it requires three things to come together:
(a) a set of events and happenings in the world, having particular identifiable characteristics (R);
(b) something beyond itself to which it refers (O);
(c) a possible meaning or interpretation in a mind, allowing that mind on recognizing R to understand O (I).
It's a 'possible' meaning in a mind for the same reason that signs in a closed book are still signs even if no mind actually interprets them. But it also has the implication that R can be a sign of O even if someone takes it to be a sign of something else, or not a sign at all. This is actually quite important for miracles. To take a famous example:
"Father, glorify your name!” Then a voice came from heaven, “I have glorified it, and will glorify it again.” The crowd that was there and heard it said it had thundered; others said an angel had spoken to him. (Jn 12:28-29 NIV)
As signs, miracles are no more immune to misinterpretation, especially deliberate misinterpretation, than any other sign, and likewise, they are no more immune to a refusal to interpret. As with every other sign, the mind has to be prepared in order to become an actual I linking R and O.
(2) There is a bad habit of assuming that if you find a 'natural explanation' for a miracle, you don't need to recognize it as a miracle. This is obviously not right in an elementary sense -- the number of 'natural explanations' that have been offered for alleged miracles but that are certainly false is very large. Merely proposing an explanation does not establish as the correct explanation. But the point goes even farther than this, because it very much matters exactly what the natural explanation explains. R is pretty much always capable of some kind of natural description because it's recognizable by our natural capacities, and all the parts of this admit of some kind of natural explanation. If water turns into wine, the behavior of the water admits entirely of a natural description, and the behavior of the wine admits entirely of a natural description. But it's also possible that the actual transformation does, as well -- for instance, assuming that it is not an instantaneous replacement of one thing by another, the transformation may well be a matter of molecules reorganizing in a way that is entirely describable by ordinary chemistry, even if it is a series of reactions and restructurings that never otherwise occur. The chemical description would in some sense be an 'explanation', but it would just explain the R's having the characteristics it does, and would be entirely inadequate to explain the actual change.
Further, a natural explanation as to the proximate causes of a change is not a natural explanation of the meaning of the change. This plays a role in what were traditionally called preternatural miracles, which are by definition events entirely within the normal course of nature, but which involve a peculiar confluence of natural events in a context that makes it meaningful. Most of the plagues of Egypt were 'just' infestations and epidemics of frogs, gnats, flies, pestilence for livestock, boils, locusts. All of these admit of natural explanation. (Indeed, people have pointed out that some of the plagues seem naturally to follow on each other -- large quantities of dead frogs could easily lead to large quantities of gnats and flies.) But when we have done so, the matter is left exactly where it was. What makes the plagues of Egypt miraculous is their meaning:
"And the Egyptians will know that I am the Lord when I stretch out my hand against Egypt and bring the Israelites out of it.” (Ex. 7:5 NIV)But nothing about the biology of frogs and flies explains the apparent meaning arising from Moses demanding that the king of Egypt let the Hebrews leave and then plagues repeatedly following when the king refuses.
(3) A common temptation in apologetics is to assume that one must first establish the possibility of miracles in general, then establish that this particular case is a miracle, and then interpret the miracle. But this fails completely to have a proper regard for miracles as signs. As a sign, a miracle must appear, i.e., R must be able to relate to I. Thus the actual path for understanding a miracle is to start with this appearance of miracle, which includes both the unusual event and the apparent meaning that can be communicated by it, then an elimination of the reasons to think it may be merely apparent. Then, finding apparent miracles that do not seem to be merely apparent, we have established the possibility of miracles in general. We do not deduce miracles from first principles any more than we deduce the existence of books from first principles; we experience them, or hear about people experiencing them, and proceed from there. First we have the apparentia, then we recognize it as an explanandum, then we determine what would be an adequate explanans.
An apparent miracle, whether the appearance is direct experience or testimonial, can only be either: (a) illusory; or (b) an unusual natural event with no significance, as in the famous case when French peasants reported to their bishop that rocks were falling from the sky, and the bishop gathered all the evidence (which later became important for the study of meteorites) but eventually closed the investigation because he could find nothing to indicate that it meant anything; or (c) a supernatural work of some created spiritual power; or (d) a divine work. If it's illusory, it will be illusory either as a matter of physical misperceiving; or as a matter of psychological misperceiving, like delusion or hallucination; or as a matter of testimonial fiction.
In other words, we find apparent miracles in the world, in a broad sense of 'apparent'; some of these turn out not to involve identifiable sensory, psychological, or testimonial defects, and therefore are genuine wonders, broadly speaking; genuine wonders with supernatural significance are supernatural wonders; and those that have efficacy, mode, or end appropriate to God are miracles in the most proper sense. Sorting all of this is just a matter of honest inquiry, although by the nature of the case the inquiry is often difficult. But it's also the case, that here, as elsewhere, we can accept any of these for the sake of following through the argument, and because miracles are signs, this is often enough for them to fulfill their function. Certainty is not a requirement for effective signification.
(4) Of what kind of thing are miracles the signs? They are signs of authority. In miracles worked directly by God this is obvious. But it is also the case in other kinds of miracles. St. Gregory the Great has a famous comment in which he says that the saints work miracles either by authority or by prayer. Miracles worked by prayer, of course, are actually worked directly under the authority of God; the role of the saint is merely per suffragium. They just put in the request, so the miracle is properly a sign of God's authority, and the prayer is just the occasion. In miracles worked by authority, however, the immediate authority signified by the miracle is that of the human being; but this sort of authority, of course, comes ultimately from God, and therefore ultimately signifies divine authority.
In the Desert of Zin (Nm. 20), Moses is told to make water come from a rock by speaking to it; he chooses instead to reprimand the children of Israel and strike the rock with his staff. Water comes from the rock, so the same result occurred. But Moses gets into very serious trouble over this -- indeed, it is given as the reason why God refuses to let him reach the Promised Land. And one way to interpret this is that Moses, in doing other than what God tells him, messes up the sign precisely as a sign of authority.