Here is a passage from a paper by Nancy Cartwright, In Favor of Laws that are not Ceteris Paribus After All, for you to break your eager heads against:
Turn now to what Earman, Roberts, and Smith call “special force laws”, like the law of universal gravitation (A system of mass M exerts a force of size GMm/r^2 on another system of mass m a distance r away) or Coulomb’s law (A system with charge q1 exerts a force of size ε0q1q2/r^2 on another system of charge q2 a distance r away). These are not strict regularities. Any system that is both massive and charged presents a counterexample. Special forces behave in this respect just like powers. This is reflected in the language we use to present these laws: one mass attracts another; two negative charges repel each other. Attraction and repulsion are not among what Ryle called ‘success’ verbs. Their truth conditions do not demand success: X can truly attract Y despite the fact that Y is not moved towards X. But perhaps, as with the delights of our universe or the Ratman’s desire for the death of his father, the requisite effects are really there after all. Earman, Roberts, and Smith feel that the arguments against this position are not compelling. I think they are: the force of size GMm/r^2 does not appear to be there; it is not what standard measurements generally reveal; and the effects we are entitled to expect –- principally an acceleration in a system of mass m a distance r away of size GM/r^2 – are not there either.
Suppose you have two massive bodies fairly close to each other. Both carry a like electrical charge. Thus both are negatively charged or both are positively charged. In virtue of Newton's inverse square law, the bodies mutually attract. But in virtue of Coulomb's law, they mutually repel. The situation envisaged seems to serve as a counterexample to the thesis that laws either are or entail strict (exceptionless) regularities. For the situation envisaged is one in which the regularity codified in 'All massive bodies mutually attract' admits exceptions when the bodies carry a sufficiently high like charge.
(Question for those of you who really know physics: the formulas Cartwright provides give scalar values, right? Don't we need vector formulations of those laws to capture the difference between attraction and repulsion, at least in the case of electrical charges? The gravitational force is always attractive, while the electrical force can be either attractive or repulsive.)
In any case, we seem to have a counterexample to the claim that all laws of nature entail exceptionless regularities. You can appreciate the relevance of this to our question about the possibility of ontic miracles. For if natural laws admit of exceptions, then this fact would seem to allow for the possibility of divine intervention in the course of nature.
But one can look at it another way. The inverse square law is operative in every region of spacetime where there are massive bodies, and Coulomb's law is operative in every region of spacetime where there are charged bodies. So these laws hold without exception. It is just that in some situations these laws are 'in competition.'
Here is a theological analogy meant to offset the theological analogy Cartwright gives in her paper. Every contingent thing that exists is continuously maintained in existence by God who is all powerful and all good. And yet there are contingent things that are evil. Are these evil things counterexamples to the divine goodness? Is the goodness of God's sustaining things in existence subject to a ceteris paribus clause? Should we say that the ongoing divine bestowal of existence is good, but not in the case of Hitler, or Stalin, or Ahmadinejad? Or should we say rather that always and everywhere to be is good, ens et bonum convertuntur, and that the divine bestowal of existence is good, but that free will is as it were a competing force so that the outcome in some cases only appears to be a counterexample to the exceptionless regularity that every bestowal of esse is good?