Criminal Law – Actus Reus & Mens Rea

  • Last updated Jul 21, 2016 5:08:56 PM
  • By Billy Sexton, Editor,, using material from Pearson's Law Express Q&A series

Actus reus and mens rea are the foundations for criminal law, so it’s really important that you get your head around the topic and related issues for when it comes to essays and exams.

Firstly, where the fudge do these two key terms of English law comes from? "Actus non facit reum nisi mens sit rea”, which literally means “an act does not make a person guilty unless mind is also guilty”.

It’s been taken that a person is guilty if they are proved to be culpable or blameworthy in both thought and action. That’s the general difference between murder and manslaughter.

You could hit and kill someone whilst driving, but if you didn’t intend to kill them, it’s manslaughter.

If it’s proven that you jumped into your car fully intending to run down some poor victim, then you’re a murderer.

However, there are complications, such as the omission to act, legal causation, intention and recklessness. 

Omission to act

Omission, or failure, to act generally carries no liabilities. That means a person can only be criminally liable where they have performed a positive act.

Let’s use the classic example of person A walking past a drowning person B. Person B can be saved if person A holds their hand. Person A doesn’t hold their hand and person B drowns. Person A is not liable.

However, there are six exceptions to this rule. The first of these is duty arising from a statute. For example, the Children and Young Persons Act 1933 makes omissions culpable by people over the age of 16 failing to look after a child under 16.

For example, if a child is not provided with adequate food or clothing (omission), this is the actus reus of that crime.

The second exemption is duty arising from special relationships. R v Gibbins and Proctor (1918), ruled that a man and his wife were guilty of murder by failing to feed the man’s daughter.

As the woman hated the daughter, this is sufficient enough to make her liable for the crime.

Thirdly, assumption of care is an exception to omission to act. Although statutory law states that parents are no longer liable for their children after the age of 16, common law, particularly, R v Chattaway (1922), imposed a duty of care upon parents where their child is over 16 but continues to reside with them and is a dependent.

The three other exceptions include official, contractual or public duties, duty to avert a danger of one's own making and failure to provide medical treatment.

Legal causation

Causation simply links conduct to a result. Factual causation is established by conducting the “But-for” test. Legal causation is a bit trickier.

The proximate cause rule can be applied. For example, you could argue that if a mechanic didn’t build a car, manslaughter wouldn’t have happened.

But this is a bit of a silly argument isn’t it? Rather, the legally liable cause lies with the one closest to the incident.

Intervening causes can also remove liability. If someone is injured by a gun shot, and then they are struck by lightning in an ambulance, you could argue the shooter is liable using the ‘but-for’ test.

However, legally, the shooter wouldn’t be liable for injuries sustained through the lightning strike.

It has been ruled in R v Cheshire (1991) that medical negligence amounts to a break in the chain of causation, unless it was “so independent” of the defendants act or “so potent” in causing death.


Intention is important because it is the mens rea requirement for serious offences, including murder. There are two types, direct intent and oblique intent.

Direct intent is relatively straightforward and is linked to the defendant’s aim or purpose. Oblique intent is where the defendant did not desire the consequences, but they knew they were certain to occur.

In R v Maloney (1985), the jury were asked to consider two questions: was murder or serious injury a natural consequence of the defendants act?

Did the defendant foresee that consequence as being a natural consequence of their act? If the answer to both are yes, the crime was intentional.


Recklessness was defined in R v Cunningham (1957) as foreseeing that a particular kind of harm may be done, but going on to do it anyway. There is also a second way of detecting recklessness, as outlined in R v Caldwell (1981).

This time, to be reckless was to carry out an act that creates obvious risk or damage and also giving no thought of there possibly being a risk, or in recognising a risk, they go on to do it anyway (#yolo).

And there we have it. Aspects of actus reus and mens rea explored on one handy webpage.

Of course, not everything is covered (so don’t blame us if everything doesn’t go according to plan), and there’s plenty more where all the above came from – namely from Pearson and their Law Express Q&A series!

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