Mala in se (“evil in itself”) – A crime or an act that is inherently immoral, such as murder, arson or rape. [Black’s Law Dictionary, 9th Ed.]
Mala prohibita (“prohibited evil”) – An act that is a crime merely because it is prohibited by statute, although the act itself is not necessarily immoral. [Black’s Law Dictionary, 9th Ed.]
Violations of the Revised Penal Code are referred to as malum in se, which literally means, that the act is inherently evil or bad or per se wrongful. On the other hand, violations of Special Laws are ‘generally’ referred to as malum prohibitum.
A common misconception is that all mala in se crimes are found in the Revised Penal Code (RPC), while all mala prohibita crimes are provided by special penal laws. In reality, however, there may be mala in se crimes under special laws, such as plunder under R.A. No. 7080, as amended. Similarly, there may be mala prohibita crimes defined in the RPC, such as technical malversation.
The better approach to distinguish between mala in se and mala prohibita crimes is the determination of the inherent immorality or vileness of the penalized act. If the punishable act or omission is immoral in itself, then it is a crime mala in se, -on the contrary, if it is not immoral in itself, but there is a statute prohibiting its commission b)”. reasons of public policy, then it is mala prohibita.
In the final analysis, whether or not a crime involves moral turpitude is ultimately a question of fact and frequently depends on all the circumstances surrounding the violation of the statute.
Dungo vs. People, G.R. No. 209464, July 1, 2015