Competency and Criminal Responsibility
This domain separates two questions that defendants confuse: can this person participate in the process now, and should the person be excused for the mental state at the time of the offence?
Competence to proceed
Dusky v United States (1960) requires sufficient present ability to consult with counsel with a reasonable degree of rational understanding, plus factual and rational understanding of the proceedings. Godinez v Moran (1993) applies the same standard to pleading guilty; Indiana v Edwards (2008) permits a higher standard for self-representation. England and Wales applies the four Pritchard (1836) limbs: understand the charge, plead to it, challenge jurors, and instruct counsel. Amnesia alone does not establish unfitness.
Responsibility
M'Naghten (1843) requires a disease of the mind producing a defect of reason such that the accused did not know the nature and quality of the act, or did not know it was wrong. R v Clarke (1939) confirms disease of the mind is a legal, not medical, concept. Automatism requires total loss of voluntary control from an external cause (R v Quick). Diminished responsibility under Homicide Act 1957 s2, as amended by Coroners and Justice Act 2009 s52, requires an abnormality of mental functioning from a recognised medical condition that substantially impaired understanding, rational judgment or self-control, and explains the killing.
Worked example
A man with a poisoning delusion kills a neighbour. If he knew he was killing a person and knew it was legally wrong, M'Naghten fails despite the delusion; diminished responsibility may still succeed if the recognised condition substantially impaired his ability to form a rational judgment.
Traps
Equating unfitness with insanity; treating delusional motive as automatic exculpation; equating intellectual disability with incompetence; forgetting the defence bears the burden on insanity and on diminished responsibility.