Sometimes it’s perfectly legal to stick knives into people. For example, surgeons do it all the time. Also, for example, if a kitchen knife is used in a legally justified act of self-defence against a violent intruder, no criminal offence is committed. Similarly, if worker in a meat factory accidentally injures a colleague with a knife while working - without any intention to do them harm - no criminal offence will have been committed. However, if someone deliberately stabs someone with criminal intent, they will have committed a crime.
It is clear that the same action - that of cutting another person with a knife - can have radically different legal consequences depending on the state of mind of the person who carried out the act. In legal parlance, the mental element of a crime is referred to as mens rea, although the expression “intent” is also commonly used.
To convict a person of most crimes, two elements must be proven beyond a reasonable doubt: Firstly, that the defendant actually physically carried out the alleged act, the actus reus. Secondly, that the defendant did that act with criminal intent, the mens rea - which translates as “guilty mind”.
If a person was provoked into a violent act, this may change how the court views the matter. For example, if there is provocation, a person charged with murder may instead only be convicted of the lesser crime of manslaughter. The law considers the state of mind of a person who has been goaded or beaten, and recognises that they may have temporarily lost full control of their actions.
Having different intent can sometimes completely change the offence committed. For example, if a car dangerously swerves across a road and kills a pedestrian, the appropriate offence is likely to be dangerous driving causing death. However, if it transpires that the driver of the car in fact spotted his mortal enemy walking down the road and deliberately swerved in order to hit him, then the driver would be charged with murder.
Another way in which the criminal law considers a person’s mental state is when they may be suffering from a mental disorder. A judge may have to first consider whether a defendant is fit to stand trial. The judge must decide whether they are able to understand the charge against them, instruct a legal team, challenge jurors and follow the evidence. If not, they may be considered unfit to stand trial, but may be remanded in psychiatric care. Alternatively, if a trial occurs, and the person is found to have committed the offence but is also found to have been insane at the time, the verdict may be not guilty by reason of insanity. This decision is made by a jury, and defendant may be committed to a psychiatric hospital.
Defendants have also been acquitted of crimes if they are found to have done them while sleepwalking. In this situation the person clearly has no criminal intent, as they were not even conscious at the time.
However, some offences deliberately exclude intent or mens rea as an element of the offence. These are called strict liability offences. For example, if you are driving down the road above the speed limit, and you genuinely did not intend to break the limit, it will be no defence to say, “I didn’t mean to do it, your honour,” even if this is true.
The immaturity of children’s minds is also the reason that - with certain exceptions - under-12s generally cannot be charged with a criminal offence.