Two rules run underneath everything that follows. Criminal law's default is subjective: it asks what this accused knew, foresaw or intended. And it must be kept apart from tort — causation and reasonableness do not mean the same things in the two subjects.
Dissecting the actus reus
The actus reus is the external, physical side of an offence, with up to three components: conduct (always — what the accused did, or exceptionally failed to do), circumstances (sometimes — the complainant's absence of consent, or that property belonged to another), and a result (sometimes — death, injury, damage).
Legislation usually specifies the result rather than the conduct. Murder under s.4 Criminal Justice Act 1964 does not tell you how to kill: it requires only that the conduct caused death, with intent to kill or cause serious injury. Rape under s.2 Criminal Law (Rape) Act 1981 has a different shape — intercourse plus absence of consent, and no result at all. So causation only matters for result crimes.
Omissions: the general rule and the duty to act
The general rule is that a mere omission does not give rise to criminal liability — the classic illustration being the infant drowning in a shallow pool while able-bodied adults look on. There are two exceptions. The first is where the offence is defined to include an omission, such as failing to disclose information under s.19 Criminal Justice Act 2011. The second is where the law recognises a duty to act, which must rest on a legally recognised basis rather than on what would be reasonable or moral.
Four bases are recognised, and each is drawn narrowly. A close family relationship can found a duty: in The People (DPP) v O'Brien Binding (IE) the duty each spouse owed the other turned on their mutual dependence, and lasted only while they lived together. A voluntary assumption of responsibility founds one too — take a vulnerable person into your care and you may not then abandon them. So does a contract whose performance protects the public. The fourth is the Miller principle: create a danger, even accidentally, become aware of it, and you must take reasonable steps to counteract it (R v Miller Persuasive (Eng)).
The law asks only for reasonable steps, never self-endangerment, and never for more than the relationship justifies.
Causation in result crimes
Causation works in two layers. Factual causation is the but-for test, which alone is far too wide. So the prosecution must also prove legal causation: an unbroken chain, undisturbed by a novus actus interveniens. The organising idea is ordinary versus extraordinary, and the Irish threshold is generous to the prosecution — it is enough that the injuries were related to the death in more than a minimal way (The People (DPP) v Davis Binding (IE)).
In practice very little is extraordinary enough. Ordinary medical treatment does not break the chain, even where it is sub-optimal, so long as the original wound remains an operating and substantial cause, and neither does the lawful withdrawal of life support. Third parties acting normally or under a lawful duty do not break it, and nor does the victim: you take your victim as you find them. The clear exception is free, informed self-administration by a responsible adult (R v Kennedy (No 2) Eng).
Mens rea and the correspondence principle
As a general rule each part of the actus reus requires a corresponding piece of mens rea: conduct requires voluntariness, a circumstance knowledge or recklessness, a result intention or recklessness. Where a component carries no mental element at all, you are looking at strict liability.
Intention
Intention is purpose — the result the accused set out to achieve. It is not desire (you can intend an outcome you would rather avoid), not motive, and not premeditation; it can be formed on the spot. In The People (DPP) v Murray Binding (IE) the Supreme Court framed it as a fixed purpose, the accused having foreseen and willed the consequence.
Being a state of mind, intention is almost always inferred from what the accused did and said, chiefly through the rebuttable presumption that a person intends the natural and probable consequences of their acts, codified for murder in s.4(2) CJA 1964. Recklessness can be evidence of intention, but it is never proof of it. The English virtual certainty test for oblique intention is not adopted by the Irish courts — use it as a persuasive tool, and say so.
Recklessness
Recklessness is the conscious taking of an unjustified risk: the accused took a risk of the relevant result or circumstance, taking it was unjustified, and the accused was actually aware of that risk. That third element is where cases turn, and it is subjective. The People (DPP) v Cagney Binding (IE) settles that recklessness is always subjective in Ireland, whatever the offence, and the same standard appears in s.2(6) Criminal Damage Act 1991 and s.16(2) Criminal Justice (Theft and Fraud Offences) Act 2001. The one exception is self-induced intoxication.
Coincidence in time
The actus reus and the mens rea must coincide. For murder it is not enough that the accused intended to kill three hours earlier; the intent must be present at the time of the conduct that caused death. Two devices soften that. Where the actus reus is a series of acts, the mens rea need coincide with only one of them (Thabo Meli v R Persuasive); where it is a continuing act, it need arise at any stage during that act (Kaitamaki v R Persuasive).
Strict liability and the presumption of mens rea
An offence is one of strict liability where a component of the actus reus carries no corresponding mens rea requirement. The mistake almost everyone makes is to reason that because a statute is silent, the offence must be strict. That is backwards: silence triggers the presumption of mens rea, which bites hardest where the offence is truly criminal rather than regulatory. Irish courts treat full mens rea as the norm and require unmistakably clear language to displace it (O'Donnell J, The People (DPP) v Ebbs Binding (IE)). Rebuttal turns on the statute's object, the seriousness of the offence and, decisively, legislative intent.
Ireland then adds something England does not have. In CC v Ireland Binding (IE) the Supreme Court held the offence under s.1(1) Criminal Law (Amendment) Act 1935 to be one of strict liability, and Hardiman J declared it inconsistent with the Constitution under Articles 38 and 40: convicting a person of a true criminal offence with no guilty mind, and exposing the blameless to life imprisonment, abrogated a right the Constitution protects. A serious strict-liability offence is therefore constitutionally vulnerable here.
Related Criminal Law notes: murder vs manslaughter · non-fatal offences against the person · accomplice liability · all free Criminal Law notes.
Start with the free General Principles module
Module 1 — actus reus, omissions, causation, mens rea, coincidence, strict liability and innocent agency — is genuinely free, with no payment and nothing to unlock. Work through it first; if it suits how you revise, the remaining eight Criminal Law modules cover homicide, non-fatal offences, sexual offences, property offences, public order, inchoate offences, parties and defences.
Frequently asked questions
What is the difference between actus reus and mens rea?
The actus reus is the external, physical part of an offence — the conduct, any required circumstance, and any required result. The mens rea is the mental element corresponding to each of those parts. Both must be proved by the prosecution beyond reasonable doubt, and neither is enough on its own.
Can you be criminally liable for doing nothing?
Only exceptionally. The general rule is that a mere omission creates no criminal liability. Liability arises where the offence is defined to include an omission, or where the accused was under a legally recognised duty to act — arising from a family relationship, a voluntary assumption of responsibility, a contract, or the Miller principle of having created the danger.
Is recklessness objective or subjective in Irish law?
Subjective. The People (DPP) v Cagney settled that recklessness is always subjective in Ireland, whatever the offence: the prosecution must prove that this accused was actually aware of the risk, not that a reasonable person would have been.
Does silence in a statute mean an offence is strict liability?
No — that is the classic error. Silence triggers a presumption that mens rea is required, and the presumption must then be rebutted, by reference to the statute's object, the seriousness of the offence and above all legislative intent. In Ireland a serious strict-liability offence is also constitutionally vulnerable, as CC v Ireland shows.
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