HideShow resource information

Elements of Insanity

  • The defence with insanity is concerned with the mental capacity of the defendant.
  • In order to be criminally liable, a defendant must be deemed sane.
  • The current rule regarding insanity comes fro the case M'Naghten(1843), stating that everyone is presumed sane, as it wound be onerous a burden if the prosecution had to prove a defendant's sanity or otherwise in every case.

CASE: R v M'Naghten (1843).

  • In order to establish a defence on the grounds of insanity it must be clearly proved that at the time of committing the act the party accused was labouring under such a defect of reason, caused by a disease of mind that they either didnt know the nature and quality of the act they were commiting or did not know that what they were doing was legally wrong.


1 of 5

Elements of Insanity

Defect of reasons

  • The defendant must show that their ability to reason was impaired.
  • This is because the basis of the defence is the defendant's deprivation of the power of reasoning. Thus a defendant who still possessed those powers but failed to use them cannot be classed as insane.

CASE: R v Clarke (1972)

Disease of the mind

  • This is a legal term and not a medical term.
  • This has caused problems at times, since the legal defenition doesnt always match the medical defenition. This is apparent when looking at the types of conditions that the courts have accepted as constituting a disease of the mind. CASE: R v Kemp (1957), R v Sullivan (1984), R v Hennessy (1989), R v Burgess(1991). These cases show the broad meaning that the courts attribute to the term 'disease of mind'.
2 of 5


Did not know the nature and quality of the act or that the act was wrong

  • The defect of reason caused by a disease of the mind must mean either that the defendant does not know the nature and quality of their act or that they dont know that the act is legally wrong.
  • In terms of the 'nature and quality act', the defendant would be unaware of their actions.
  • If the defendant is aware of what they are doing it is still posssible to rely on the defence if they do not know that what they are doing is legally wrong.

CASE: R v Windle (1952)

Burden of proof

  • The defendant must prove that they were suffering from insanity when they committed the offence. This must be proved on a balance of probabilities.
3 of 5


The burden of proof rests with the defendant

  • Critics argue that it is unfair that the burden is on the defendant to prove that they are suffering from insanity. They say that this undermines the notion that the defendant is innocent until proven guilty by the prosecution.

The use of a legal rather than a medical defenition

  • The main flaw within this defence is that the courts use a legal defenition instead of a medical one. This dates from 1843, remaining firmly rooted in that era in terms of its understanding of insanity and failing to take into account the changes since then.

The rules are to broad

  • The classification of diabetics, epileptics and sleepwalkers as being classed as insane has been criticised for suggesting that they are a danger to the public, which is far from true in the vast majority of cases.


4 of 5


Place the burden of proof on the prosecution

  • The Butler committee and the Criminal Law Revision Committee have suggested that, since it is part of the mens rea, the burden of proof should be reversed and placed on the prosecution rather than on the defendant.

A new defence

  • Critics believe that we should abolish the M'Naghten rule and introduce a new defence. They suggest that it should apply to defendants with a mental disorder and should result in verdict of 'not guilty on evidence of a mental disorder'. This would avoid the defendant being labelled insane.
5 of 5


william johnston


yes your work is apauling if anything it has lowered my grades

william johnston


most certainly

william johnston


@ bryan bernal you are extrememly uninteligent almost as bad as her !!! 

william johnston


james is so correct in every way ask your teacher and dont be a failure

william johnston


i have to go now and actually learn and be educated and normal plaease gain acess to a proper education

charlie harrison


very unhelpful



This was exactly what I was looking for, thanks for uploading.

Similar Law resources:

See all Law resources »See all Law of Tort resources »