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10.4 Self-defence

Commonwealth Criminal Code: Guide for practitioners

10.4 Self-defence

(1) A person is not criminally responsible for an offence if he or she carries out the conduct constituting the offence in self- defence.

(2) A person carries out conduct in self-defence if and only if he or she believes the conduct is necessary:

  1. (a) to defend himself or herself or another person; or
  2. (b) to prevent or terminate the unlawful imprisonment of himself or herself or another person; or
  3. (c) to protect property from unlawful appropriation, destruction, damage or interference; or
  4. (d) to prevent criminal trespass to any land or premises; or
  5. (e) to remove from any land or premises a person who is committing criminal trespass;
    and the conduct is a reasonable response in the circumstances as he or she perceives them.

(3) This section does not apply if the person uses force that involves the intentional infliction of death or really serious injury:

  1. (a) to protect property; or
  2. (b) to prevent criminal trespass; or
  3. (c) to remove a person who is committing criminal trespass.

(4) This section does not apply if:

  1. (a) the person is responding to lawful conduct; and
  2. (b) he or she knew that the conduct was lawful.

However, conduct is not lawful merely because the person carrying it out is not criminally responsible for it.


Conduct which would otherwise amount to an offence is not criminal if it is done in self defence. Chapter 2 extends the application of the defence beyond circumstances involving a threat of personal harm. A plea of self defence is also available when action is taken to defend property or to repel or remove trespassers. That enlargement of the range of interests which are included within the plea of self defence is parallelled by a corresponding enlargement of the range of offences which can be excused by a plea of self defence. Though it is often assumed that self defence is limited in its applications to offences which involve the use of force, Chapter 2 imposes  no limit of this kind on the range of offences for which self defence might provide an excuse or justification. A judicious lie might amount to a far  more effective defensive measure than a resort to force as, for example, when property is threatened with unlawful appropriation. If the lie was told in circumstances which could amount to an offence, there is no apparent reason why a defendant should not resort to s10.4 to excuse or justify their conduct.

Conduct is only excused on the ground of self defence if it was a reasonable response to threatened harm. The defendant is judged, however, on their own perceptions of the threat. An unreasonable mistake can provide the  basis for a complete defence.

The defence has no application in cases where the defensive action was a response to conduct which the defendant knew to be lawful. Moreover,  death or serious injury, if caused intentionally, cannot be excused if the defendant’s use of deadly force was undertaken in defence of real or personal property.

Chapter 2 extends the meaning of “self defence” well beyond ordinary usage. It includes defence of a stranger and extends to action taken to prevent or terminate unlawful imprisonment. Self defence also extends to defence of  real and personal property and prevention of trespass or removal of trespasses from land or premises.

Unlike 10.2 Duressand 10.3 Suddenand extraordinary emergency, both of which require a reasonable apprehension of threatened harm, self defence is available even in circumstances where the defendant responded to an unreasonable apprehension of harm.264 The more unreasonable the tale of mistake, however, the more likely it is that it will be rejected by a the trier of fact as incredible.265

Though the defendant is allowed the benefit of the defence when action is taken in response to an honest albeit unreasonable perception of threatened harm, the response to that perceived harm must be reasonable

Section 10.4 follows common law in its recognition that there are circumstances in which deadly force might be an excusable response to “injury, violation, or indecent or insulting usage”.266 Self defence against threatened harm to the person does not require equality between the threat and the response. However, when interests other than personal safety are threatened, s10.4 limits the defence. It has no application in cases where death or personal injury is intentionally caused in defence of real or personal property,  but there is no barrier to reliance on the defence when the charge  is one of attempting to cause death or serious harm in defence of property.

Self defence cannot excuse the use of force in order to avoid a threat of personal injury, property damage or trespass to land which is known to arise from the lawful conduct of another person. So, for example, conduct which would contravene one of the provisions in Ch7 - Division 147 – Causing harm to Commonwealth public officials cannot be excused on grounds of self defence if the victim of the offence is known to be acting lawfully. Note the distinction between self defence against lawful conduct and self defence against conduct which is merely excusable.  So long as the defendant does   no more than is reasonable in the circumstances, defensive measures can be taken against threats by individuals who are known to be irresponsible by reason of immaturity or mental impairment.

  1. Compare s15D, Criminal Law Consolidation Act 1935 (SA) and s46 Criminal Code Act 1924 (Tas) which adopt the same approach. This acceptance of subjectivity is modified, however, when an unreasonable apprehension of harm is the result of self-induced intoxication: 8.4 Intoxication (relevance to defences).

  2. Compare 9.1 Mistake or ignorance of fact (fault elements other than negligence). Though the provi- sion, which is concerned with fault rather than defences, has no application in such a case, the same principle applies, as a matter of commonsense.

  3. 266 Howe (1958) 100 CLR 448, 460 (Dixon CJ).