In criminal cases, there exists two elements: a guilty mind (mens rea) and a guilty act (actus reus). Do these two Latin terms require a preceding article, and which would it be (definite/indefinite)?

Here is a contextual example:

[The/An] actus reus can be proven in this instance; [the/a] mens rea, less so.

  • If we could substitute guilty feelings and guilt for the two terms, it's clear that you can dispense with the articles: Guilt can be proven in this instance; guilty feelings, less so. I'd guess that the Latin terms can be handled similarly.
    – Lawrence
    Feb 24, 2016 at 1:28
  • If you use Ngram to search for legal texts using these terms, you'll see that sometimes an article is used and sometimes not. "an actus reus..." or "the actus reus" or just bare "actus reus".
    – TRomano
    Mar 15, 2016 at 18:02

3 Answers 3


It's hard to say whether the article is required, since in Latin they're assumed and not explicitly expressed.

A quick swing through relevant web loci shows that usage with articles is fairly common. It looks like it could go either way.

From nationalparalegal.edu:

Mens rea, or "guilty" intent, deals with what the defendant needs to have been thinking at the time he or she committed the actus reus for criminal liability to attach. In order to be guilty of most crimes, the defendant must have had the mens rea required for the crime he was committing at the time he committed the criminal act. As with the actus reus, there is no single mens rea that is required for all crimes. Rather, it will be different for each specific crime.


When referring to either in a general sense, an article is not required. I'm pretty sure this is true of all legal doctrines or terms that are in Latin.

Res Judicata

Res ipsa loquitur

See a more comprehensive list here.

In all other cases, the rules of articles apply.

The prosecution has not proffered sufficient evidence to satisfy the mens rea required under Section Blah of Statute Whatever.

His killing John Doe is an actus reus that satisfies the actus reus required under Section Blah of Statute Whatever.


Checking with Ngram can be helpful, it appears that the articles both determinative indeterminative) are generally used to refer accordingly to a more or less specific cases. I think they follow general the rules of the English language on the usage of articles.

Usage examples:

  • Conduct must be voluntary If the accused is to be found guilty of a crime, his or her behaviour in committing the actus reus must have been voluntary. Criminal Law

  • The essential elements of a crime are a physical act, often referred to as the actus reus (wrongful act), and the intent or state of mind, frequently called the mens rea (guilty mind). To establish that a defendant is guilty of..

  • Where a defendant is under a legal duty to act his mere failure to act might give rise to the commission of an actus reus. The imposition of criminal liability is based on an assumption that a defendant's acts or omissions at the time of the alleged ...Cases and Materials on Criminal Law

  • Actus reus means the ''guilty act.''The prosecution must prove that the defendant voluntarily committed a prohibited act.Suppose Mary Jo files an insurance claim for a stolen car, knowing that her car was not stolen. That is insurance fraud, ...Business Law

  • You can get plottable results for "mens rea," "a mens rea," and "the mens rea" on your Ngram chart if you use rea in place of reas. The level of article usage for the two terms that Dog Lover asks about seems pretty high to me, considering that (as ChongDogMillionaire points out), "res judicata" and "res ipsa loquitur" very rarely draw a preceding article.
    – Sven Yargs
    Mar 15, 2016 at 21:54

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