Malum prohibitum (plural mala prohibita, literal translation: "wrong [as or because] prohibited") is a Latin phrase used in law to refer to conduct that constitutes an unlawful act only by virtue of statute, as opposed to conduct evil in and of itself, or malum in se. Conduct that was so clearly violative of society's standards for allowable conduct that it was illegal under English common law is usually regarded as "malum in se". An offense that is malum prohibitum, for example, may not appear on the face to directly violate moral standards.
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 feel that murder of other human beings is wrong, regardless of whether a law governs such conduct or where the conduct occurs, and is thus recognizably malum in se. In contrast, consider driving laws. In the U.S., people drive on the right-hand side of the road. In the UK and other states of the Commonwealth, people drive on the left-hand side. Violation of these rules is an example of a malum prohibitum law because the act is not inherently bad, but is forbidden by law, as set forth by the lawmakers of the jurisdiction. Malum prohibitum crimes are criminal not because they are inherently bad, but because the act is prohibited by the law of the state.
This concept was used to develop the various common law offences. It may be criticized by remarking that if murder and rape may be considered generally defined as crimes, the inclusion of different behaviors that can be punished under such indictments is culturally variable (see marital rape, statutory rape, infanticide).