Is there a clear-cut distinction between something that is "immoral" and something that is "impolite"? After all, aren't both categories about violating a society's norms?

Quick example: in this country, it's impolite to slurp your soup; not so in some other countries. That's just a matter of differing social norms

Killing innocent people is immoral; it's immoral regardless of where you are, and not just because we happen to have a social norm against it.

Being impolite can also be a moral error, though usually not a big one. It's wrong to upset people for no good reason, and being impolite sometimes has that effect. But it's not just that we have a social custom of not distressing people for no good reason; it's wrong.

Two small points. First, the moral claims above could be subject to qualifications; I leave it to you to consider what such qualifications might be. Second, I haven't argued that it's wrong to distress people for no reason, though the fact that no one one likes having it done to them would be part of any such argument. I also haven't argued that killing innocents is just plain wrong, but similar reasons would apply there with even more force.

In any case, a big part of the distinction is that if we all agree that something is impolite, that pretty much makes it so. But even if we all agree that something is wrong—or right—we could all be mistaken. For example: same-sex intimate relationships weren't wrong even when everyone thought otherwise. Everyone was confused, and the result was a lot of needless misery. The social norms were moral mistakes, albeit wide-spread ones.

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