Malum in se
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Malum in se (plural mala in se) is a Latin phrase meaning wrong or evil in itself. The phrase is used to refer to conduct assessed as sinful or inherently wrong by nature, independent of regulations governing the conduct. It is distinguished from malum prohibitum, which is wrong only because it is prohibited.
For example, most human beings believe that murder, rape, and theft are wrong, regardless of whether a law governs such conduct or where the conduct occurs, and is thus recognizably malum in se. In contrast, malum prohibitum crimes are criminal not because they are inherently bad, but because the act is prohibited by the law of the state. For example, most United States jurisdictions require drivers to drive on the right side of the road. This is not because driving on the left side of a road is considered immoral, but because consistent rules promote safety and order on the roads.
Another way to describe the underlying conceptual difference between "malum in se" and "malum prohibitum" is "iussum quia iustum" and "iustum quia iussum", namely something that is commanded (iussum) because it is just (iustum) and something that is just (iustum) because it is commanded (iussum).