Is murder illegal because its wrong?Or is murder wrong because its illegal?
a great question -- a deep one, and an old one -- basically grounded in the classic theistic question addressed by Plato (in Euthyphro) and many others since -- does God command us not to do things (such as murder) because they're wrong, or are they wrong (simply) because God commands us not to do them ... Stephen's response is excellent, but I'll offer another angle. Re the first half -- is murder illegal b/c it's wrong -- no doubt those legislators who have illegalized murder are at least partly (maybe primarily/exclusively) motivated by its wrongness (that's the sociological/empirical question) -- but presumably your question is meant to be more general, i.e. not merely restricted to murder, whose 'wrongness' most everyone can agree to (though not everyone). If you were to ask 'of all those things that are illegal, are they illegal b/c they are wrong?' surely for many/most of them the answer would be 'no.' It's illegal to go through a red light, not b/c going thru red lights is morally wrong but b/c the powers that be, in their wisdom, have established various conventions for the smooth/safe running of society, so they've set up traffic laws to that end -- just which legislation is motivated by morality and which by (say) the need for societal conventions is an empirical question -- but no doubt both factors play at least some role in much legislation ... (and other factors as well) ... re the sec on half -- 'is murder wrong b/c it's illegal' -- Stephen is right to stress the fundamental distinction between law and morality, but I'll just add one point -- the case might be made that, in general, it's morally wrong to break the laws of your society (all else being equal) -- so at least PART of the wrongness of murder (perhaps a very small part) would consist in the fact that committing it is to break the laws ... (again, generalizing the topic: running a red light IS probably wrong precisely because it's illegal ...) Now of course there are some important complicated cases -- for example, civil disobedience -- in some cases you might argue it's 'right' to break the law -- if you think the law itself is morally wrong -- but that's handled by the 'all else being equal' clause I mentioned ....
hope that's useful!