Insanity and automatism

Criminal liability requires voluntary conduct by a responsible agent. Two defences address involuntary acts: insanity (governed by the M'Naghten Rules) and automatism. The crucial distinction turns on the internal/external factor test: if involuntariness stems from an internal cause (disease of the mind), the defence is insanity, yielding a special verdict with potential supervision; if from an external cause, it is automatism, yielding outright acquittal. This bifurcation reflects policy concerns about dangerousness and recurrence rather than medical logic.

M'Naghten's Case (1843) 10 Cl & Fin 200: Established the insanity test requiring proof of (1) defect of reason (2) from disease of the mind (3) such that defendant did not know nature/quality of act or that it was wrong. Foundation of modern law.

R v Quick [1973] QB 910: Hypoglycaemia from insulin injection (external) is automatism; crystallised internal/external distinction. Critical for diabetes cases.

R v Sullivan [1984] AC 156: Epilepsy is disease of the mind despite being organic/physical condition. Legal not medical concept; policy drives classification.

R v Hennessy [1989] 1 WLR 287: Hyperglycaemia from diabetes itself (internal) is insanity not automatism. Stress doesn't externalise internal condition.

R v Burgess [1991] 2 QB 92: Sleepwalking from internal disorder is insanity. Policy factors (recurrence risk, need for supervision) influence classification.

First identify whether defendant claims insanity or automatism. For insanity: (1) D bears legal burden (balance of probabilities); (2) Apply M'Naghten's three elements methodically - was there defect of reason? From disease of mind? Did D know nature/quality OR wrongness?; (3) 'Wrong' means legally wrong (Windle), not morally.

For automatism: (1) D bears evidential burden only; (2) Must show total loss of voluntary control (not mere impairment); (3) Trace cause - if internal (epilepsy, diabetes, sleepwalking), redirect to insanity; if external (blow, injection), proceed; (4) Check for self-induced automatism (Bailey) - no defence to basic intent if reckless.

Burden confusion: Insanity requires D to prove on balance of probabilities; automatism only evidential burden on D.

'Nature and quality' ≠ moral character: Refers to physical act only. If D knows he's cutting throat, he knows nature/quality even if thinks justified.

Diabetes classification: Hypoglycaemia (external insulin) = automatism; hyperglycaemia (internal lack of insulin) = insanity.

Total loss required: Automatism needs complete absence of control, not just impairment or 'blackout'.