It’s especially important to differentiate morality and law, inasmuch as discussion of the moral and legal often conflate. On the one hand, the two differ since we believe some legal acts to be immoral, and some laws to be unjust. And even if the law didn’t prohibit murder, stealing, and the like, we would probably still consider them wrong. This suggests that the two aren’t co-extensive. On the other hand, the two are connected because the law embodies many moral precepts. Legal prohibitions incorporate most of our ordinary moral rules such as those against lying, killing, cheating, raping, and stealing. This suggests there is some connection between the moral and the legal.
Though it’s possible to have morality without law, or law without morality, the two usually go together. Therefore, we suggest that law codifies morality. In other words, the law formulates the culture’s morality into legal codes. Again, not every legal code refers to a moral issue, but most laws do have some moral significance. Though a connection between the moral and legal exists, they clearly aren’t the same things.
While a thing’s illegality may give us a reason not to do the thing, this is a prudential rather than moral reason. In other words, if we are afraid to steal because we might get caught, then we fear punishment, not immorality. Nevertheless, we might offer moral reasons to abide by the law. We could say that we owe it to the state to abide by their laws and that civil disobedience undermines both the moral fabric and our tacit agreement with the state. This was essentially Socrates’ argument against escaping from Athens before his impending execution. But in general, legal arguments aren’t applicable to ethical discussion. Ethicists generally discuss morality, not legality, as will we.