Criminal Law: Text, Cases, and Materials (9th edn)
Jonathan Herring
p. 66 2. Actus Reus: The Conduct Element
Jonathan Herring, Professor of Law, Exeter College, Oxford
https://doi.org/10.1093/he/9780198848479.003.0002
Published in print: 04 May 2020
Published online: September 2020
Abstract
The actus reus is a central aspect of criminal law that defines the harm done to the victim and the
wrong performed by the defendant. In many cases this involves proof that the defendant caused a
particular result. This chapter begins by distinguishing the component elements of a crime. It
then discusses the voluntary act ‘requirement’; causation; classification of offences; the need for a
voluntary act; omissions; and seeking a coherent approach to causation.
Keywords: criminal law, English law, crime, criminal behaviour, voluntary act, causation,
offences, omissions
Central Issues
1. The traditional method of analysing the definition of an offence is to separate out the actus reus
(which describes the acts of the defendant and their consequences) and the mens rea (which
describes the required mental state of the defendant).
2. A defendant is only guilty if she or he has performed a voluntary act.
3. Normally people will not be guilty of a crime because they omitted to act. However, they can be
guilty for an omission if they were under a duty to act.
4. Many crimes require proof that the defendant caused a particular result. A defendant will be
held to have caused a result if but for his or her actions the result would not have occurred and
there has been no intervening act of a third party.
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, Part I: The Law
1 Distinguishing the Component Elements of a Crime
Definition
Actus reus: the conduct element of the offence. The actus reus describes what the defendant
must be proved to have done (or sometimes failed to do), in what circumstances, and with what
consequences in order to be guilty of a crime.
Mens rea: the mental element of the offence. This may be, for example, intention, recklessness,
or negligence.
p. 67 ↵ The traditional way of analysing criminal offences is to divide a crime up into the conduct of the
accused (known as the actus reus or conduct element) and the state of mind of the accused (the mens
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rea or mental element). For example, in a murder case the prosecution must show that the defendant
caused the death of the victim and that he or she intended to kill or cause grievous bodily harm to the
victim. The actus reus of murder is causing the death of the victim; the mens rea is an intention to kill
or cause grievous bodily harm. Only if both the actus reus and mens rea are proved will the defendant
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be guilty. In this chapter we will consider the actus reus, and in Chapter 3 the mens rea will be
discussed. In Part II of this chapter we will examine the benefits and disadvantages of dividing crimes
into the mens rea and actus reus elements. →1 (p.101)
So what is the actus reus of a crime? One popular way of explaining it is to define its role, namely that
it identifies the conduct which the criminal law considers harmful. The actus reus of an offence tells us
what we can and cannot do: killing, damaging another’s property, and injuring another person are
examples of forbidden kinds of conduct. By contrast the mens rea and defences enable us to decide
whether defendants were to blame for their wrongful acts. Another popular way of defining an actus
reus is by describing what it is not: the actus reus is that part of the crime which is not concerned with
the accused’s state of mind.
The exact nature of the actus reus depends on the particular crime: in murder it involves killing; in
theft it involves taking another’s property. The actus reus of a crime may involve three different
aspects:
(1) proof that the defendant did a particular act,
(2) proof that the act caused a particular result, and
(3) proof that the act or result occurred in certain circumstances.
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Not all actus rei3 involve all three of these. For example, the offence of bigamy requires the act of
marriage in certain circumstances (the defendant is already married), but there is no need to prove
any result. It is useful to distinguish between conduct crimes and result crimes:
(1)
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, Conduct crimes require proof only that the defendant did an act. There is no need to
demonstrate that the act produced a particular result. Possession of prohibited drugs would be
an example.
(2) Result crimes require proof not only that the defendant performed a particular act but that that
act produced certain results. For example, murder requires proof that the defendant’s act
caused the death of the victim.
Are there any common threads that link the actus reus of every crime? There is much debate over this
issue and this chapter will now consider three particular questions:
(1) Do all actus rei require an act?
p. 68 (2) Do all actus rei require a voluntary act?
(3) If the actus reus of a crime requires proof that the defendant caused a particular result, what
does ‘cause’ mean?
2 The Voluntary Act ‘Requirement’
Definition
The ‘voluntary act requirement’: many criminal offences require proof that the defendant
performed a voluntary act. But not all do: sometimes offences can be committed by an omission,
some only require proof of a state of affairs, and sometimes a defendant can be convicted in
respect of the actions of another.
Usually you cannot commit a crime without doing an act. Sitting in a room thinking the most evil of
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thoughts and conjuring up the most heinous of plans is not an offence. Indeed if evil thoughts were to
constitute criminal offences, the prisons would be very full indeed! Not only must there be an act;
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there must be a voluntary act. Lord Denning explained: ‘[T]he requirement that it should be a
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voluntary act is essential … in every criminal case’. Where the defendant is not acting voluntarily he
or she is said to be acting as an automaton and will not be guilty of an offence because both the mens
rea and actus reus will not be proved. If Barbara was holding a valuable vase when Andre came up
behind her and said ‘boo’ in a loud voice, causing Barbara to drop the vase, then this (the dropping of
the vase) would not be seen as Barbara’s act, and so she could not be convicted of unlawfully
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damaging the vase. The detail of the law on automatism, or involuntary acts, is discussed in detail in
Chapter 12. →2 (p.103)
The general principle that a crime must involve an act of the defendant is subject to two important
caveats. First, it is far from clear what is meant by the word ‘act’ here. The question how to define an
act will be considered in detail in Part II of this chapter. Second, there are a number of crimes which
appear to be exceptions to the rule. In fact there are so many exceptions that some commentators
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argue that the rule does not really exist. In brief, the exceptions include the following:
(1) Sometimes a failure to act, an omission, can give rise to criminal liability. In such cases omission
can constitute the actus reus of the crime.
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, (2) Sometimes the actus reus of an offence is defined as a state of affairs or set of circumstances,
which may or may not involve an actual act. For example, possession of a firearm can, in some
circumstances, amount to an offence.
(3) Under some circumstances a defendant can be responsible for the acts of another person.
p. 69 ↵
It should be noted that whether these are or are not true exceptions in part depends on how one
defines an act. Let us now consider these exceptions to the ‘rule’ that a criminal offence must require
an act in more detail.
2.1 Omissions
Generally a person will not be liable for simply failing to act. Criminal lawyers often point out that if a
person comes across a child drowning in a pond and simply walks by leaving the child to die, there is
no criminal liability. Some countries have statutes that make it a criminal offence not to offer aid to
those you come across who are in peril, when it is reasonably practical for you to do so. But there is no
such general duty in English and Welsh law. This is not to say that a defendant is never criminally
liable for an omission: a defendant can be criminally liable for an omission where there is a duty to act
in a particular way.
Definition
A summary of the criminal law on omissions: a defendant (D) is only guilty of a crime when
failing to act, where
D is under a duty to act
D breached the duty
D’s breach caused the harm to the victim.
The discussion of liability for omissions will be divided into five sections. First, we will note that there
are some crimes which can never be committed by omission. Second, we will consider when a
defendant will be under a duty to act. Third, we will ask what is required of a defendant who is under
such a duty. Fourth, we will explore when the breach of duty causes the harm. Fifth, the difficult
question of how acts and omissions can be distinguished will be tackled. →3 (p.107)
Crimes that cannot be committed by omission
There are certain crimes that cannot be committed by an omission. These are statutory crimes which
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in their definition require an act to be committed. For example, in Ahmad the defendant was charged
with an offence under the Protection from Eviction Act 1977 which required proof of the defendant
‘doing acts calculated to interfere with [the victim’s] peace and comfort’. The defendant, a landlord,
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