Mens rea
Etymology
A Latin phrase meaning "guilty mind," from mens, "mind," and rea, the feminine of reus, "defendant, guilty one." It comes from the maxim actus non facit reum nisi mens sit rea — "the act does not make a person guilty unless the mind is also guilty." It names the mental element the prosecution must usually prove alongside the act.
noun phrase · /menz-RAY-uh/
The guilty state of mind — the intent or knowledge — that a person must have to be criminally responsible for an act.
What it names
The reason intent matters in a courtroom — why the same physical act can be murder, manslaughter, or an accident depending on what was in the person’s head.
Example
Without proof of mens rea, the shooting could be a tragic accident rather than a crime.
Related idea
Mens rea is the guilty mind; actus reus is the guilty act, and most crimes require both to be proved together.