出典:Wiktionary
From Latin mēns + reus (字義どおりに “guilty mind”), from the English common law precept Actus non facit reum nisi mens rea sit ("The act does not make a person guilty unless the mind is also guilty").
In common law legal systems (those of England かつ its former colonies), different jurisdictions make different classifications of degree of guilt (levels of mens rea). In the highest classification, the guilty party intentionally committed the act in full knowledge of its consequences and that it was an offence; lower classifications imply lower degrees of intention (such as intentionally undertaking a course of action of which the offence was a likely result). In cases of strict liability and absolute liability offences, no proof on mens rea is required by the prosecution.