Right of self-defense
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|Part of the common law series|
|Other common law areas|
|Rights by beneficiary|
|Other groups of rights|
The right of self-defense (also called, when it applies to the defense of another, alter ego defense, defense of others, defense of a third person) is the right for persons to use reasonable force or defensive force, for the purpose of defending one's own life or the lives of others, including, in certain circumstances, the use of deadly force.
If a defendant uses defensive force because of a threat of deadly or grievous harm by the other person, or a reasonable perception of such harm, the defendant is said to have a "perfect self-defense" justification. If defendant uses defensive force because of such a perception, and the perception is not reasonable, the defendant may have an "imperfect self-defense" as an excuse.
"Justification does not make a criminal use of force lawful; if the use of force is justified, it cannot be criminal at all." 
The early theories make no distinction between defense of the person and defense of property. Whether consciously or not, this builds on the Roman Law principle of dominium where any attack on the members of the family or the property it owned was a personal attack on the pater familias – the male head of the household, sole owner of all property belonging to the household, and endowed by law with dominion over all his descendants through the male line no matter their age. The right to self-defense is phrased as the principle of vim vi repellere licet ("it is permitted to repel force by force") in the Digest of Justitian (6th century).
In Leviathan (1651), Hobbes (using the English term self-defense for the first time) proposed the foundation political theory that distinguishes between a state of nature where there is no authority and a modern state. Hobbes argues that although some may be stronger or more intelligent than others in their natural state, none are so strong as to be beyond a fear of violent death, which justifies self-defense as the highest necessity. In the Two Treatises of Government, John Locke asserts the reason why an owner would give up their autonomy:
...the enjoyment of the property he has in this state is very unsafe, very unsecure. This makes him willing to quit a condition, which, however free, is full of fears and continual dangers: and it is not without reason, that he seeks out, and is willing to join in society with others, who are already united, or have a mind to unite, for the mutual preservation of their lives, liberties and estates, which I call by the general name, property.
In earlier times before the development of national policing, an attack on the family home was effectively either an assault on the people actually inside or an indirect assault on their welfare by depriving them of shelter and/or the means of production. This linkage between a personal attack and property weakened as societies developed but the threat of violence remains a key factor. As an aspect of sovereignty, in his 1918 speech Politik als Beruf (Politics as a Vocation), Max Weber defined a state as an authority claiming the monopoly on the legitimate use of physical force within defined territorial boundaries. Recognizing that the modern framework of nations has emerged from the use of force, Weber asserted that the exercise of power through the institutions of government remained indispensable for effective government at any level which necessarily implies that self-help is limited if not excluded.
For modern theorists, the question of self-defense is one of moral authority within the nation to set the limits to obedience to the state and its laws given the pervasive dangers in a world full of weapons. In modern societies, states are increasingly delegating or privatizing their coercive powers to corporate providers of security services either to supplement or replace components within the power hierarchy. The fact that states no longer claim a monopoly to police within their borders, enhances the argument that individuals may exercise a right or privilege to use violence in their own defense. Indeed, modern libertarianism characterizes the majority of laws as intrusive to personal autonomy and, in particular, argues that the right of self-defense from coercion (including violence) is a fundamental human right, and in all cases, with no exceptions, justifies all uses of violence stemming from this right, regardless whether in defense of the person or property. In this context, note that Article 12 Universal Declaration of Human Rights states:
No one shall be subjected to arbitrary interference with his privacy, family, home or correspondence, nor to attacks upon his honour and reputation. Everyone has the right to the protection of the law against such interference or attacks.
However, United Nations human rights oversight bodies have not recognized self-defense as a human right. The right to self-defense and human rights may share roots in natural law, but they are ultimately of a different nature and have different functions. The right to self-defense is a genuinely pre-societal right that evolved in the absence of the state. It survived the formation of the state because no state will ever have enough power to perfectly protect individuals. Conversely, human rights evolved in response to the overbearing presence of the state and they primarily serve to ensure that states do not accumulate too much power. Unlike human rights, self-defense also does not incorporate a vision to transform the state. It can accommodate any type of state, including authoritarian states that fail to respect human rights. 
The inclusion of defense of one's family and home recognizes the universal benefit claimed to stem from the family's peaceable possession of private property. This general approach implicitly attacks Hohfeld's focus on the correlative relationship between right and duty as an aspect of human interactiveness as opposed to rights deemed implicitly more important because they attach to a person by virtue of his or her ownership of property. Further, it follows that, in this moral balancing exercise, laws must simultaneously criminalize aggression resulting in loss or injury, but decriminalize qualitatively identical violence causing loss or injury because it is used in self-defense. As a resolution of this apparent paradox and in defiance of Hohfeld, Robert Nozick asserted that there are no positive civil rights, only rights to property and the right of autonomy. In this theory, the "acquisition principle" states that people are entitled to defend and retain all holdings acquired in a just way and the "rectification principle" requires that any violation of the first principle be repaired by returning holdings to their rightful owners as a "one time" redistribution. Hence, in default of self-defense in the first instance, any damage to property must be made good either in kind or by value. Similarly, theorists such as George Fletcher and Robert Schopp have adopted European concepts of autonomy in their liberal theories to justify the right-holder using all necessary force to defend his or her autonomy and rights. This right inverts the felicitation principle of utilitarianism with the responsive violence being the greatest good to the individual, but accurately mirrors Jeremy Bentham who saw property as the driving force to enable individuals to enhance their utilities through stable investment and trade. In liberal theory, therefore, to maximise the utility, there is no need to retreat nor use only proportionate force. The attacker is said to sacrifice legal protection when initiating the attack. In this respect, the criminal law is not the tool of a welfare state which offers a safety net for all when they are injured. Nevertheless, some limits must be recognized as where a minor initial attack simply becomes a pretext for an excessively violent response. The civil law systems have a theory of "abuse of right" to explain denial of justification in such extreme cases.
Defense of others
|Part of the common law series|
|Liability and remedies|
|Duty to visitors|
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The rules are the same when force is used to protect another from danger. Generally, the defendant must have a reasonable belief that the third party is in a position where they would have the right of self-defense. For example, a person who unknowingly chances upon two actors practicing a fight would be able to defend their restraint of the one that appeared to be the aggressor. However, in many jurisdictions a person who causes injury in defense of another may be liable to criminal and civil charges if such defence turned out to be unnecessary.
Model Penal Code
Common law cases
In People v. La Voie, Supreme Court of Colorado, 395 P.2d 1001 (1964), The court wrote, "When a person has reasonable grounds for believing, and does in fact actually believe, that danger of his being killed, or of receiving great bodily harm, is immanent, he may act on such appearances and defend himself, even to the extent of taking human life when necessary, although it may turn out that the appearances were false, or although he may have been mistaken as to the extent of the real actual danger."
Definition in specific countries
- Castle doctrine
- Gun politics
- Imperfect self-defense
- Justifiable homicide
- Ossian Sweet
- Son assault demesne
- Use of force continuum
- Criminal Law Cases and Materials, 7th ed. 2012; John Kaplan, Robert Weisberg, Guyora Binder
- Dennis J. Baker, Glanville Williams Textbook of Criminal Law (London: 2012) at Chapter 21.
- See generally, Frier & McGinn, A Casebook on Roman Family Law, Oxford University Press (2004).
- Jan Arno Hessbruegge, Human Rights and Personal Self-Defense in International Law, Oxford University Press (2017), ch. 3 https://global.oup.com/academic/product/human-rights-and-personal-self-defense-in-international-law-9780190655020?cc=us&lang=en&
- Carpenter, Catherine L. (2003). "Of the Enemy Within, The Castle Doctrine, and Self-Defense". Marquette Law Review. 86 (4): 653–700.
- Sir Edward Coke, The First Part of the Institutes of the Laws of England, or, A Commentary on Littleton (London, 1628, ed. F. Hargrave and C. Butler, 19th ed., London, 1832)
- Dressler, Joshua, New Thoughts About the Concept of Justification in the Criminal Law: A Critique of Fletcher's Thinking and Rethinking, (1984) 32 UCLA L. Rev. 61.
- Fletcher, George P. (1990) Crime of Self-Defense: Bernhard Goetz and the Law on Trial, Chicago: University of Chicago Press, ISBN 0-226-25334-1.
- Fletcher, George P. (2000) Rethinking Criminal Law, Oxford: Oxford University Press, ISBN 0-19-513695-0.
- Getman, Julius G; Marshall, F Ray (2001). "The Continuing Assault on the Right to Strike". Texas Law Review. 79 (3): 703.
- Green, Stuart P. (1999). "Castles and Carjackers: Proportionality and the Use of Deadly Force in Defense of Dwellings and Vehicles". University of Illinois Law Review. 1999 (1).
- Hessbruegge, Jan Arno, Human Rights and Personal Self-Defense in International Law, Oxford University Press (2017) https://global.oup.com/academic/product/human-rights-and-personal-self-defense-in-international-law-9780190655020?cc=us&lang=en&
- McCoy, Scott D. (2001). "The Homosexual-Advance Defense and Hate Crimes Statutes: Their Interaction and Conflict". Cardozo Law Review. 22 (2): 629.
- Maguigan, H. (1991). "Battered Women and Self-Defense: Myths and Misconceptions in Current Reform Proposals". University of Pennsylvania Law Review. 140 (2): 379–486. doi:10.2307/3312349. JSTOR 3312349.
- Nourse, V. F. (2001). "Self-Defense and Subjectivity". The University of Chicago Law Review. 68 (4): 1235–1308. doi:10.2307/1600480. JSTOR 1600480.
- Schopp, Robert F. (1998) Justification Defenses and Just Convictions, Cambridge: Cambridge University Press, ISBN 0-521-62211-5.
- Segev, Re'em (2005). "Fairness, Responsibility and Self-Defense". Santa Clara Law Review. 45 (2): 383–460.
- Semeraro, (2006) Osservazioni sulla riforma della legittima difesa
- Vitu, Legitime defense et infraction d'imprudence, Revue de Science Criminelle, 1987, 865.