Affirmative defense in the context of "Justification and excuse"

In a legal dispute, one party has the burden of proof to show that they are correct, while the other party has no such burden and is presumed to be correct. The burden of proof requires a party to produce evidence to establish the truth of facts needed to satisfy all the required legal elements of the dispute. It is also known as the onus of proof.

The burden of proof is usually on the person who brings a claim in a dispute. It is often associated with the Latin maxim semper necessitas probandi incumbit ei qui agit, a translation of which is: "the necessity of proof always lies with the person who lays charges." In civil suits, for example, the plaintiff bears the burden of proof that the defendant's action or inaction caused injury to the plaintiff, and the defendant bears the burden of proving an affirmative defense. The burden of proof is on the prosecutor for criminal cases, and the defendant is presumed innocent. If the claimant fails to discharge the burden of proof to prove their case, the claim will be dismissed.

Imperfect self-defense is a common law doctrine recognized by some jurisdictions whereby a defendant may mitigate punishment or sentencing imposed for a crime involving the use of deadly force by claiming, as a partial affirmative defense, the honest but unreasonable belief that the actions were necessary to counter an attack. Not all jurisdictions accept imperfect self-defense as a basis to reduce a murder charge.

• Self-defense: A perfect argument of self-defense proves all elements of self-defense, and results in the defendant's acquittal. If a defendant proves imperfect self-defense, the defendant will be convicted of a lesser homicide charge, such as voluntary manslaughter.
• Imperfect self-defense: The concept of imperfect self-defense is that, although not all elements of self-defense were proved, extenuating circumstances nonetheless partially excuse the act that caused death.