Thinking Citizen Blog—Mens Rea, Res Ipsa: Who Knows? Who Cares? Who Should?

Thinking Citizen Blog — Saturday is Justice, Freedom, Law, and Values Day

Today’s Topic: Mens Rea, Res Ipsa: Who Knows? Who Cares? Who Should?

Mens rea is Latin for “guilty mind.” “The standard common law test of criminal liability is expressed in the Latin phrase actus reus non facit reum nisi mens sit rea, i.e. “the act is not culpable unless the mind is guilty”. Does this make sense to you? For all crimes or just some? How about for “civil wrongs” (“torts”) which are “private wrongs” punishable by fines and damage awards rather than prison terms or the death penalty? Or do you feel that intentions don’t matter so much as the consequences and that the perpetrator of an act with harmful results should be held liable no matter what? One technical term for this is “res ipsa” or “the act speaks for itself.” Another is “strict liability” — the idea that liability should not depend on the degree of negligence of the perpetrator. Today a few more details. Experts — please chime in. Correct, elaborate, elucidate.


1. “By the late 1950s to early 1960s, the common law of mens rea was widely acknowledged to be a slippery, vague, and confused mess. This was one of several factors that led to the development of the Model Penal Code.” The latter is not law itself but has been adopted as law by many legislatures including in New York and New Jersey. The code distinguishes between five levels of mental culpability: strict liability (mental state irrelevant), negligently, recklessly, knowingly, and purposefully. (for details see first link below)

2. “The general rule under common law and statutory law is that ignorance of the law or a mistake of law is no defense to criminal prosecution. However, in some cases, courts have held that if knowledge of a law, or if intent to break a law, is a material element of an offense, then a defendant may use good faith ignorance as a defense.”

3. “A good faith belief belief that a law is unjust or unconstitutional is no excuse but “reasonable reliance on an official statement of law, afterward determined to be invalid or erroneous” does not constitute a criminal act.”

NB: “In the United States, a law must be reasonably clear; it must be worded so that a reasonable layman can comprehend the specific prohibited acts. Otherwise, the law may be unconstitutional pursuant to the vagueness doctrine.”


1. “Subjective: where the court must be satisfied that the accused actually had the requisite mental element present in his or her mind at the relevant time.”

2. “Objective: where the requisite mens rea element is imputed to the accused. on the basis that a reasonable person would have had the mental element in the same circumstances.”

3. “Hybrid: where the test is both subjective and objective.”


1. “The event does not normally occur unless someone has acted negligently

2. “The evidence rules out the possibility that the actions of the plaintiff or a third party caused the injury.”

3. “The type of negligence in question falls within the scope of the defendant’s duty to the plaintiff.”

CONCLUSION — three questions for lawyers

1.) What is the your favorite case involving issues of mens rea, res ipsa, or strict liability?

2.) Did you ever change your mind on the subject?

3.) If so, why?

NB: A landmark case involving “mens rea” was Morissette v US (1952) involving a recycler and World War II veteran (Morissette) convicted of stealing spent bomb casings from an Air Force bombing range. The Supreme Court voted to overturn his conviction — unanimously.

Mens rea — Wikipedia

Res ipsa loquitur — Wikipedia

Model Penal Code — Wikipedia

Animus nocendi — Wikipedia

Voluntas necandi — Wikipedia

Vagueness doctrine — Wikipedia

Morissette v. United States — Wikipedia

Morissette v. United States [SCOTUSbrief Landmark Edition]

For the last four years of posts organized by theme:

PDF with headlines — Google Drive

Two special attachments below:

#1 A graphic guide to justice (9 metaphors on one page).

#2 “39 Songs, Prayers, and Poems: the Keys to the Hearts of Seven Billion People” — Adams House Senior Common Room Presentation, 11/17/20


Please share the coolest thing you learned in the last week related to justice, freedom, the law or basic values. Or the coolest, most important thing you learned in your life related to justice, freedom, the law, or basic values. Or just some random justice-related fact that blew you away.

This is your chance to make some one’s day. Or to cement in your mind something that you might otherwise forget. Or to think more deeply about something dear to your heart.

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