Moral laws are often claimed to be laws only in a metaphorical sense since there are clear differences between them and laws of nature. Laws of nature allegedly brook no exceptions, but we can always (or nearly always) envision exceptions to moral laws, cases in which it would be allowed to ignore a particular prohibition. There is a moral law to tell the truth, but if we are hiding Jews from the Nazis we don't have to tell them about it (there's a disturbing case of this in The Hiding Place by Corrie Ten Boom). The point is that moral laws are not absolute while physical laws are.
However, I think this is a misunderstanding. The exceptions to moral laws are cases where one moral law comes into conflict with another. The moral law that we should preserve life has more authority than the law that tells us to tell the truth, so we lie to the Nazi who asks us if we are hiding any Jews. But there are exact parallels with physical laws. The law of gravity dictates that the magnet will fall to the ground, unless the law of electromagnetism dictates that it will stick to the side of the refrigerator. The second law overrules the first in this case. This doesn't say anything against gravity. The law of gravity, when stated strictly, is defined in a vacuum, with no other forces in play -- that is, it is defined with all other things being equal (ceteris paribus). This is the same with moral laws. These laws are being described in a moral vacuum, where no other moral issues are in play. If the only moral thing at issue is whether to tell the truth or not, there is a moral law that says we should tell the truth, ceteris paribus. If other moral issues come into the picture, then they may interfere with it so that it will no longer be the case that we should tell the truth, in the same way that if other physical forces are in play, an object may no longer obey the law of gravity by falling towards the center of mass.
Of course, there's another way in which physical laws and moral laws are dissimilar: we can choose whether or not we obey moral laws but, for the most part, we cannot choose whether or not we obey physical laws. I say "for the most part" because I can choose to jump up and thereby thwart the law of gravity for a few moments, but if I jump off a cliff I can't choose to stop falling. Whether that means moral laws can only be considered "laws" in a metaphorical sense is something I leave to my readers. Perhaps it's the physical laws that are the metaphors.
(cross-posted at Agent Intellect)
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