Imperfect self-defense is a common law

Common law

Common law is law developed by judges through decisions of courts and similar tribunals rather than through legislative statutes or executive branch action...

 doctrine of criminal procedure

Criminal procedure

Criminal procedure refers to the legal process for adjudicating claims that someone has violated criminal law.-Basic rights:Currently, in many countries with a democratic system and the rule of law, criminal procedure puts the burden of proof on the prosecution – that is, it is up to the...

 recognized by some jurisdictions whereby a defendant

Defendant

A defendant or defender is any party who is required to answer the complaint of a plaintiff or pursuer in a civil lawsuit before a court, or any party who has been formally charged or accused of violating a criminal statute...

 may mitigate punishment

Punishment

Punishment is the authoritative imposition of something negative or unpleasant on a person or animal in response to behavior deemed wrong by an individual or group....

 or sentencing

Sentence (law)

In law, a sentence forms the final explicit act of a judge-ruled process, and also the symbolic principal act connected to his function. The sentence can generally involve a decree of imprisonment, a fine and/or other punishments against a defendant convicted of a crime...

 imposed for a crime involving the use of deadly force

Deadly force

Deadly force, as defined by the United States Armed Forces, is the force which a person uses, causing—or that a person knows, or should know, would create a substantial risk of causing—death or serious bodily harm...

 by claiming, as a partial affirmative defense

Affirmative defense

A defendant offers an affirmative defense when responding to a plaintiff's claim in common law jurisdictions, or, more familiarly, in criminal law. Essentially, the defendant affirms that the condition is occurring or has occurred but offers a defense that bars, or prevents, the plaintiff's claim. ...

, the honest but unreasonable belief that the actions were necessary to counter an attack.

Effect

—Answers.com

It may also be used to make a plea bargain

Plea bargain

A plea bargain is an agreement in a criminal case whereby the prosecutor offers the defendant the opportunity to plead guilty, usually to a lesser charge or to the original criminal charge with a recommendation of a lighter than the maximum sentence.A plea bargain allows criminal defendants to...

 to a lesser included offense

Lesser included offense

A lesser included offense, in criminal law, is a crime for which all of the elements necessary to impose liability are also elements found in a more serious crime....

.

Examples in common law - United States

For example, in the U.S. state of California

California

California is a state located on the West Coast of the United States. It is by far the most populous U.S. state, and the third-largest by land area...

 a defendant can be convicted of manslaughter

Manslaughter

Manslaughter is a legal term for the killing of a human being, in a manner considered by law as less culpable than murder. The distinction between murder and manslaughter is said to have first been made by the Ancient Athenian lawmaker Dracon in the 7th century BC.The law generally differentiates...

 but not murder

Murder

Murder is the unlawful killing, with malice aforethought, of another human being, and generally this state of mind distinguishes murder from other forms of unlawful homicide...

 when imperfect self-defense applies.

The doctrine of imperfect self-defense recognizes a defendant’s honest but unreasonable belief that deadly force is needed. An appellate court in Kansas

Kansas

Kansas is a US state located in the Midwestern United States. It is named after the Kansas River which flows through it, which in turn was named after the Kansa Native American tribe, which inhabited the area. The tribe's name is often said to mean "people of the wind" or "people of the south...

 held that "Imperfect self defense is an intentional killing committed with an unreasonable but honest belief that circumstances justified deadly force."

Another court, in Maryland

Maryland

Maryland is a U.S. state located in the Mid Atlantic region of the United States, bordering Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware to its east...

, held that:

—State v. Faulkner, 483 A.2d 759,769 (Md. 1984)

Michigan also recognizes imperfect self-defense as a qualified defense that can mitigate second-degree murder to voluntary manslaughter. However, the doctrine can only be used where the defendant would have had a right to self-defense but for the fact that the defendant was the initial aggressor.