Actus non facit reum nisi mens sit rea

The maxim expresses the basic principle of criminal liability: a person is not ordinarily guilty of a crime merely because he did a prohibited act; the act must be accompanied by a guilty mind. Criminal liability thus has two components, the actus reus, the physical conduct or omission with its consequences, and the mens rea, the mental element the law requires for that offence.

Indian criminal statutes do not adopt the maxim in general terms. Instead, the mental element is written into each definition through words such as intentionally, knowingly, voluntarily, dishonestly, fraudulently, with reason to believe, or rashly and negligently. Several of these are defined in Section 2 of the BNS; dishonestly and fraudulently, for instance, are in Section 2(7) and 2(9). The General Exceptions in Chapter III reflect the same idea from the other side: acts of a child under seven (Section 20), of a person of unsound mind incapable of knowing the nature of the act (Section 22), and of a person intoxicated against his will (Section 23), and acts done by accident (Section 18) or under a mistake of fact in good faith (Sections 14 and 17), are not offences because the guilty mind is missing.

For statutory offences the Supreme Court has held that mens rea is presumed to be an ingredient unless the statute excludes it expressly or by necessary implication, as in Nathulal v. State of Madhya Pradesh (1966). Where the subject matter, the language and the object of a regulatory or public welfare law show that liability is meant to be strict, the presumption is displaced, as in State of Maharashtra v. Mayer Hans George (1965). Strict and absolute liability offences are therefore the main exceptions to the maxim.

The maxim is distinct from motive, which is the reason for an act and is generally irrelevant to guilt, and from ignorantia juris non excusat, which denies a defence based on ignorance of law. Examiners usually ask for its meaning or for the two elements it implies.