What is the difference between mental illness and insanity?
According to the McNaughten rule insanity is a legal term use to describe individuals who are unable to determine between right and wrong at the time of committing a crime. A mentally ill individual might still be able to determine between right and wrong but instead of being classified as insane they are simply described as having a mental illness.
The McNaughten rule cannot be used to defend the actions of a person who drinks alcohol and then murders someone. Why not?
An individual is not able to use the McNaughten rule if they have committed a murder while intoxicated because the state of being intoxicated is the result of a voluntary choice made by the individual. The individual made a conscious decision to drink alcohol, which they knew could cause them to have an altered mental status.