There's a question on this site regarding what a rational person should accept as a miracle, but the question and its answers seem to take the definition and categorization (as well as consequence) of a 'miracle' for granted.
Hume defined a miracle as a violation of a law of nature (a law being how nature is expected to behave). However, how would we identify such an event? In the days of Aristotelian physics, many considered magnets to be 'miraculous' (or magical, what have you), because they violated the law of nature that for one body to affect another those two bodies would have to be in physical contact with one another. Imagine if Einstein (or anyone else) had come along to hypothesize relativity, and Herbert Ives and G.R. Stilwell conducted experiments and made observations that were incompatible with the current model of physics (see experimental evidence for relativity). Would we call the subjects of their observations miracles?
A more precise definition of 'violation' in this context might be 'a non-repeatable counter-instance' of natural laws. However, then we're stuck with a similar problem: imagine that Ives and Stilwell were unable to repeat their results. Would they then call it a miracle? No, they would attribute it to error (human error, measurement/instrumental error, etc.) On the other hand, of course, if they could repeat their results they would also not call their observations miraculous (or magic, or whatever), they'd propose a new scientific theory to fit their observations.
Therefore, I ask, what is a miracle, and why should a miracle be an impetus for changing our metaphysical views (i.e. posit that a God or similar being exists as a force greater than nature, etc.) instead of revising our physical (as in, scientific) ones?
EDIT: actually, looking more carefully at the answers here, it seems like this issue is addressed. The question therefore is directed at those who do believe in (at least the possibility of) miracles