Criminal Law: Defenses

Under what circumstances is a defendant justified in using deadly force in self-defense?

A defendant is justified in using deadly force in self-defense only if they reasonably believe that such force is necessary to prevent imminent death or great bodily harm to themselves.

What is the difference between the 'duty to retreat' and 'stand your ground' jurisdictions?

In 'duty to retreat' jurisdictions, a person must retreat before using deadly force if they can do so safely, except in their own home (Castle Doctrine). In 'stand your ground' jurisdictions, a person has no duty to retreat before using deadly force if they are lawfully present.

How does the modern 'reasonable belief' rule for defense of others differ from the common law 'alter ego' rule?

Under the modern 'reasonable belief' rule, a defendant is justified in using force to defend another if they reasonably believe the third party is entitled to use force. The common law 'alter ego' rule required the defendant to step into the shoes of the third party, meaning they were only justified if the third party was actually justified.

Can a defendant use deadly force solely to protect uninhabited property, and what landmark case established this rule?

No, a defendant cannot use deadly force (such as a spring gun) solely to protect uninhabited property, as human life is valued over property. This principle was famously established in Katko v. Briney.

What is the 'necessity' (or choice of evils) defense in criminal law?

The necessity defense applies when a defendant commits a crime to prevent a greater imminent harm from occurring, provided the defendant did not create the situation and there was no legal alternative.

Is necessity a valid defense to intentional murder, and what famous English case illustrates this?

Necessity is generally never a valid defense to intentional murder, as established in Regina v. Dudley and Stephens, where starving shipwrecked sailors killed and ate a cabin boy.

What are the two prongs of the M'Naghten rule for the insanity defense?

Under the M'Naghten rule, a defendant is legally insane if, due to a mental disease or defect, they either (1) did not know the nature and quality of their act, or (2) did not know that what they were doing was wrong.

How does the Irresistible Impulse test expand upon the M'Naghten rule?

The Irresistible Impulse test expands upon M'Naghten by adding a volitional component, allowing an insanity defense if a mental disease or defect prevented the defendant from controlling their actions, even if they knew the act was wrong.

What is the Model Penal Code (MPC) 'Substantial Capacity' test for insanity?

The MPC Substantial Capacity test states a defendant is not responsible if, due to mental disease or defect, they lacked the 'substantial capacity' to either appreciate the criminality (wrongfulness) of their conduct or conform their conduct to the requirements of the law.

What is the Durham rule (or 'product test') for insanity, and why is it rarely used today?

The Durham rule states that a defendant is not criminally responsible if their unlawful act was the 'product of mental disease or defect.' It is rarely used because it is considered too broad and gives too much power to psychiatric experts.