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The non-aggression principle (NAP)—also called the non-aggression axiom, the zero aggression principle (ZAP), the anti-coercion principle, or the non-initiation of force—is a moral stance which asserts that aggression is inherently illegitimate. NAP and property rights are closely linked, since what aggression is depends on what a person's rights are. Aggression, for the purposes of NAP, is defined as the initiation or threatening of violence against a person or legitimately owned property of another. Specifically, any unsolicited actions of others that physically affect an individual’s property or person, no matter if the result of those actions is damaging, beneficial, or neutral to the owner, are considered violent or aggressive when they are against the owner’s free will and interfere with his right to self-determination or the principle of self-ownership.
Supporters of the NAP often appeal to it in order to explain the immorality of theft, vandalism, assault, and fraud. In contrast to nonviolence, the non-aggression principle does not preclude violence used in self-defense or defense of others. Many supporters argue that NAP opposes such policies as victimless crime laws, taxation, and military drafts. NAP is the foundation of most present-day libertarian philosophies.
The principle has been derived by various philosophical approaches, including:
- Argumentation Ethics: Some modern libertarian thinkers ground the non-aggression principle by an appeal to the necessary praxeological presuppositions of any ethical discourse, an argument pioneered by libertarian scholar Hans Hermann Hoppe. They claim that the act of arguing for the initiation of aggression, as defined by the non-aggression principle is contradictory. Among these are Stephan Kinsella and Murray Rothbard.
- Consequentialism: Some advocates base the non-aggression principle on rule utilitarianism or rule egoism. These approaches hold that though violations of the non-aggression principle cannot be claimed to be objectively immoral, adherence to it almost always leads to the best possible results, and so it should be accepted as a moral rule. These scholars include David Friedman, Ludwig von Mises, and Friedrich Hayek.[not in citation given]
- Natural rights: Some derive the non-aggression principle by appealing to natural rights that are deemed a natural part of man. Such approaches often reference self-ownership, ethical intuitionism, or the right to life. Thinkers in the natural law tradition include John Locke, Lysander Spooner, and Murray Rothbard.
- Social contract: The social contract is an intellectual device intended to explain the appropriate relationship between individuals and their governments. Social contract arguments assert that individuals unite into political societies by a process of mutual consent, agreeing to abide by common rules and accept corresponding duties to protect themselves and one another from violence and other kinds of harm. Many libertarians, however, reject the "social contract" term as it has been historically used in a non-voluntary fashion. They argue that for a contract to be enforceable it must be voluntarily accepted.
- Social progress: Herbert Spencer, the 19th century polymath, first proposed that aggression either between individuals or the state against the individual inhibits sociocultural evolution. Based on his theory of social evolution (from Lamarckian use-inheritance), he concluded that aggression in all its forms impedes progress by interfering with the individual's ability to exercise his or her faculties. He wrote, "... when each possesses an active instinct of freedom, together with an active sympathy—then will all the still existing limitations to individuality, be they governmental restraints, or be they the aggressions of men on one another, cease. ... Then, for the first time in the history of the world, will there exist beings whose individualities can be expanded to the full in all directions. And thus, as before said, in the ultimate man perfect morality, perfect individuation, and perfect life will be simultaneously realized."
- Objectivism: Ayn Rand rejected natural or inborn rights theories as well supernatural claims and instead proposed a philosophy based on observable reality along with a corresponding ethics based on the factual requirements of human life in a social context. She stressed that the political principle of non-aggression is not a primary and that it only has validity as a consequence of a more fundamental philosophy. For this reason, many of her conclusions differ from others who hold the NAP as an axiom or arrived at it differently. She proposed that man survives by identifying and using concepts in his rational mind since "no sensations, percepts, urges or instincts can do it; only a mind can." She wrote, "since reason is man's basic means of survival, that which is proper to the life of a rational being is the good; that which negates, opposes or destroys it [i.e. initiatory force or fraud] is the evil."
Definitional issues 
Many supporters and opponents of abortion rights justify their position on NAP grounds. The central question to determine whether or not abortion is consistent with NAP is at what stage of development a fertilized human egg cell can be considered a human being with the status and rights attributed to personhood. Some supporters of NAP argue this occurs at the moment of conception. Others argue that since the fetus lacks sentience until a certain stage of development, it doesn't qualify as a human being, and as such may be considered property of the mother. Opponents of abortion, on the other hand, state sentience is not a qualifying factor. They refer to the animal rights discussion and point out the Argument from Marginal Cases that concludes NAP also applies to non-sentient (i.e. mentally handicapped) humans.
Objectivist philosopher Leonard Peikoff has argued that a fetus has no rights over its host because it is a parasite. Pro-choice libertarian Murray Rothbard had the same stance. Other pro-choice supporters base their argument on criminal trespass. In that case, they claim, NAP is not violated when the unborn child is forcibly removed, with deadly force if need be, from the mother’s body, just as NAP is not violated when an owner removes from the owner’s property an unwanted visitor who is not willing to leave voluntarily. Libertarian Walter Block follows this line of argument but makes a distinction between evicting the fetus and killing it (see Libertarian perspectives on abortion).
Anti-abortion libertarians, however, argue that because the parents were actively involved in giving life to another human being, and the unborn child was brought inside the mother’s body by both parents’ action and without the child’s consent, no parasitism or trespassing is involved. They state that as the parents are responsible for the position the child is in, NAP would be violated when the child is killed with abortive techniques.
Intellectual property rights 
NAP is defined as applicable to any unauthorized actions towards a person’s physical property. Supporters of NAP disagree on whether it should apply to intellectual property (IP) as well. Those who don't think so claim IP can be copied by others without any harm to the originator. The argument reflects an analysis of the fundamental reason behind property rights, scarcity. Some claim ideas are not scarce because if A "takes" an idea of B, he does not prevent B from retaining the idea. Others state ideas are just as scarce as any other commodity since it requires time, money and labor to develop an original idea. If other people decide to use the idea they also make unauthorized use of the effort of the originator, which would violate NAP. Those who think that NAP should be applied to IP in the same way as to physical property argue that all IP is somehow sublimated in physical property and that any owner has the right to determine what is done with his physical property.
For example, if a software engineer writes a program on his own computer a copy of this program can only be obtained by using the engineer’s computer (either directly or remote via the internet). If the engineer then burns his program onto a DVD-ROM and sells this DVD to a third party he may sell this product unconditionally (i.e. the sale is free of any restrictions for the DVDs use) or, as would be normal in most cases, under specific conditions (i.e. the sale only transfers user rights and limited copyright). In the latter case, unauthorized copying would violate NAP as the engineer co-owns the DVD and a third party cannot make a copy without using the engineer’s property.
Though NAP is meant to guarantee an individual’s sovereignty, libertarians greatly differ on the conditions under which NAP applies. Especially unsolicited intervention by others, either to prevent society from being harmed by the individual’s actions or to prevent an incompetent individual from being harmed by his or her own (in)actions, is an important issue. The debate centers on topics like the age of consent for children, intervention counseling (i.e. for addicted persons, or in case of domestic violence), involuntary commitment and involuntary treatment with regards to mental illness, medical assistance (i.e. prolonged life support vs euthanasia in general and for the senile or comatose in particular), human organ trade, state paternalism (including economic intervention) and foreign intervention by states. Other discussion topics on whether intervention is in line with NAP include nuclear weapons proliferation, and human trafficking and (illegal) immigration.
Supporters generally argue that NAP only applies to humans, because humans generally have a free will and a self-conscious and rational mind, as well as a moral understanding. Most humans can therefore understand NAP and can be held accountable for their actions. Some critics claim that although these abilities are common they are not universal characteristics of the species. Young children and mentally handicapped persons may not have them (e.g. a person in a coma). When NAP applies to them as well as to normal people, as supporters of NAP agree, critics state that logically NAP should apply to all life forms with similar characteristics (see the Argument from Marginal Cases). This stance would lead to similar rights for sufficiently intelligent animals.
The argument extends to intelligent artificial life as well, such as AI computers and AI robots. Transhumanists argue that when artificial organs and mind uploading eradicate the boundaries between humans and machines NAP will automatically apply to all intelligent life.
Some supporters justify the state on the grounds that anarchism implies that the non-aggression principle is optional because the enforcement of laws is open to competition. They claim competing law enforcement would always result in war and the rule of the most powerful. Anarcho-capitalists usually respond to this argument that this presumed outcome of coercive competition (e.g. PMCs or PDAs that enforce local law) is not likely because of the very high cost, in lives and economically, of war. They claim that war drains those involved and leaves non-combatant parties as the most powerful, economically and militarily, ready to take over. Therefore, anarcho-capitalists claim that in practice, and in more advanced societies with large institutions that have a responsibility to protect their vested interests, disputes are most likely to be settled peacefully (e.g. through DROs).
Anarcho-capitalists also point out that a state monopoly of law enforcement does not necessarily make NAP present throughout society as corruption and corporatism, as well as lobby group clientelism in democracies, favor only certain people or organizations. Anarcho-capitalists generally argue that the state violates the non-aggression principle by its nature because governments use force against those who have not stolen private property, vandalized private property, assaulted anyone, or committed fraud.
Panarchists view a state as compatible with NAP as long as citizenship is not compulsory and all its citizens support its governance voluntarily. Statists, on the other hand, claim a state has legal jurisdiction over a certain area of land, or even owns that land. In that case NAP is not violated if a state imposes rules and regulations, any, as long as people entering the area are aware of these conditions and those already inside who disagree with unilaterally changed conditions are free to leave. The anarcho-capitalist argument that persons born in the land area owned or regulated by a state never were able to agree with the state's conditions and have no obligation to comply usually is countered by the statist argument that as the parents agreed to submit their child to these conditions of stay the child can only hold its parents responsible, not the state.
Some libertarians see taxes as a violation of NAP while others argue that because of the free-rider problem in case security is a public good, enough funds would not be obtainable by voluntary means to protect individuals from aggression of a greater severity. They therefore accept taxation, and consequently a breach of NAP with regard to any free-riders, as long as no more is levied than is necessary to optimise protection of individuals against aggression. Geolibertarians argue a land value tax is compatible with NAP.
Anarcho-capitalists argue that the protection of individuals against aggression is a service like any other and that it can be supplied by the free market much more effectively and efficiently than by a government monopoly. Their approach, based on proportionality in justice and damage compensation, argues that full restitution is compatible with both retributivism and a utilitarian degree of deterrence in order to uphold NAP in society. They extend their argument to all public goods and services that require taxation, like security offered by dikes.
|300's BC||Epicurus||"Natural justice is a symbol or expression of usefullness, to prevent one person from harming or being harmed by another."|
|900's||Abu Mansur Maturidi, Ibn Qayyim Al-Jawziyya, Averroes||These Islamic theologians and philosophers wrote that man could rationally know that man had a right to life and property.|
|early 1200s||Ibn Tufail||In Hayy ibn Yaqdhan the Islamic philosopher discussed the life story of a baby living alone without prior knowledge who discovered natural law, and natural rights, which obliged man not to coerce against another's life or property. Ibn Tufail influenced Locke's notion of Tabula rasa.|
|1682||Samuel von Pufendorf||In On the Duty of Man and Citizen he wrote "Among the absolute duties, i.e., of anybody to anybody, the first place belongs to this one: let no one injure another. For this is the broadest of all duties, embracing all men as such."|
|1689||John Locke||In Second Treatise on Government he wrote "Being all equal and independent, no one ought to harm another in his life, health, liberty, or possessions."|
|1722||William Wollaston||In The Religion of Nature Delineated he formulated "No man can have a right to begin to interrupt the happiness of another." This formulation emphasized "begin" to distinguish aggressive disturbances from those in self-defense ("...yet every man has a right to defend himself and his against violence, to recover what is taken by force from him, and even to make reprisals, by all the means that truth and prudence permit.")|
|1790||Mary Wollstonecraft||In "A Vindication of the Rights of Men" Mary Wollstonecraft states: "The birthright of man ... is such a degree of liberty, civil and religious, as is compatible with the liberty of every other individual with whom he is united in a social compact, and the continued existence of that compact."|
|1816||Thomas Jefferson||"No man has a natural right to commit aggression on the equal rights of another, and this is all from which the laws ought to restrain him." (Thomas Jefferson to Francis Gilmer, 1816)|
|1851||Herbert Spencer||In Social Statics, he proposed the law of equal freedom - "Every man has freedom to do all that he wills, provided he infringes not the equal freedom of any other man." - as the best political arrangement to promote social progress. This being the implication of his theory of human social evolution he developed from Lamarckian use-inheritance.|
|1859||John Stuart Mill||The harm principle formulated in On Liberty, states that "the only purpose for which power can be rightfully exercised over any member of a civilized community, against his will, is to prevent harm to others."|
|1961||Ayn Rand||In an essay called "Man's Rights" in the book "The Virtue of Selfishness" she formulated "The precondition of a civilized society is the barring of physical force from social relationships. ... In a civilized society, force may be used only in retaliation and only against those who initiate its use."|
|1963||Murray Rothbard||"No one may threaten or commit violence ('aggress') against another man's person or property. Violence may be employed only against the man who commits such violence; that is, only defensively against the aggressive violence of another. In short, no violence may be employed against a nonaggressor. Here is the fundamental rule from which can be deduced the entire corpus of libertarian theory." Cited from "War, Peace, and the State" (1963) which appeared Egalitarianism as a Revolt Against Nature and Other Essays|
Natural law theorist Murray Rothbard traces the non-aggression principle to natural law theorist St. Thomas Aquinas and the early Thomist scholastics of the Salamanca school. This, in turn, may be seen in relation to Aquinas' view on greed, "a sin against God, just as all mortal sins, in as much as man condemns things eternal for the sake of temporal things", and on envy, which be defined as "sorrow for another's good" (cf. Seven deadly sins).
Early formulations that use terms such as "harm" or "injury," such as those of Epicurus and Mill above, are today generally considered imprecise. "Harm" and "injury" are too subjective; one man's harm may be another man's benefit. For example, a squatter may make "improvements" that the owner considers detrimental. Modern formulations avoid such subjectivity by formulating the NAP in terms of individual rights or observable conduct (initiation of force/violence).
In modern social-political culture advocating civil liberties, laissez-faire markets, and limited government, i.e. by the US Libertarian Party (US LP) and by Young Americans for Liberty (YAL), similar formulations of NAP are commonplace (see the libertarian pledge).
||This section may contain original research. (May 2012)|
||This section needs additional citations for verification. (May 2012)|
NAP faces two kinds of criticism: the first holds that the principle is immoral, the second argues that it is impossible to apply consistently in practice; respectively, consequentialist or deontological criticisms, and inconsistency criticisms.
Moral criticisms 
Some critics argue that the non-aggression principle is unethical because it opposes the initiation of force even when the results of such initiation would be better (though not necessarily for each and every individual involved) than any other course of action. Suppose, for example, that you could save a million lives by killing one innocent person. The non-aggression principle holds that you should not kill that person, which is consistent with a non-collectivist, non-utilitarian worldview. However, this leads to a million deaths, which, according to utilitarian philosophers such as John Stuart Mill, is morally reprehensible. Advocates of NAP argue that milder forms of the same dilemma (for example, the choice between taking away part of a wealthy person's property or allowing a poor person to starve) are useful in explaining the validity of the NAP, as the above situation would constitute theft.
Furthermore, opponents of NAP must demonstrate why it is preferable for a poor person not to starve at the expense of a wealthy person's property before the argument can be evaluated. Another response to this argument would be that no one has a positive right to be saved. Some critics see the denial of positive rights as unethical but most libertarians argue that positive rights conflict with the right to self-ownership and self-determination of every individual and would legitimize some form of slavery.
Innocent persons problem 
Some critics use the example of the trolley problem to invalidate NAP. In case of the runaway trolley, headed for five victims tied to the track, NAP does not allow a trolley passenger to flip the switch that diverts the trolley to a different track if there is a person tied to that track. That person would have been unharmed if nothing was done, therefore by flipping the switch NAP is violated. Another example often cited by critics is human shields.
Some supporters argue that no one initiates force if their only option for self-defense is to use force against a greater number of people as long as they were not responsible for being in the position they are in. Murray Rothbard's and Walter Block's formulations of NAP avoid these objections by either specifying that the NAP applies only to a civilized context (and not 'lifeboat situations') or that it applies only to legal rights (as opposed to general morality). Thus a starving man may, in consonance with general morality, break into a hunting cabin and steal food, but nevertheless he is aggressing, i.e. violating the NAP, and (by most rectification theories) should pay compensation. Critics argue that the legal rights approach might allow people who can afford to pay a sufficiently large amount of compensation to get away with murder. They point out that local law, though based on NAP, may vary from proportional compensation to capital punishment to no compensation at all.
Supporters generally argue that any harm done to innocent persons or any other collateral damage in these cases is done by whoever or whatever caused this situation to occur. In this view, if the threatened party harms the innocent persons, NAP is not violated. Furthermore, some supporters argue that actions that minimize harm are consistent with NAP.
Non-physical violence 
Other critics state that NAP is unethical because it legitimizes non-physical violence, such as mental battering, defamation, boycotting, and discrimination. If a victim thus provoked would turn to physical violence, according to NAP, he would be labeled an aggressor. Supporters of NAP, however, state that defamation constitutes freedom of speech and the boycotting or discrimination that may follow constitutes other people's freedom to believe what they like and deal with whoever they like. Supporters also state that individuals most of the time voluntarily engage in situations that may cause mental battering. Some supporters point out that mental battering, when it cannot be avoided, comes down to unauthorized physical overload of the senses (i.e. eardrum and retina) and NAP does apply.
Many supporters consider verbal threats of imminent physical violence sufficient justification for a defensive response in a physical manner. Such threats would then constitute a limit to the freedom of speech. Property owners can also pose a limitation on the freedom of speech (i.e. the owner of a movie theater may prohibit anyone inside to call ‘fire!’ without reason, to avoid a stampede; the owner of a bank, however, cannot prevent anyone from urging the general public to a bank run).
H.L. Mencken, a writer who influenced many libertarians, puts an ethical limit on the freedom of speech:
|“||I believe there is a limit beyond which free speech cannot go, but it's a limit that's very seldom mentioned. It's the point where free speech begins to collide with the right to privacy. I don't think there are any other conditions to free speech. I've got a right to say and believe anything I please, but I haven't got a right to press it on anybody else. [...] Nobody's got a right to be a nuisance to his neighbors.||”|
Inconsistency criticisms 
Environmental pollution 
Critics argue it is not possible to uphold NAP when protecting the environment as most pollution can never be traced back to the party that caused it. They therefore claim that only general broad government regulations will be able to protect the environment. Supporters cite the problem of the tragedy of the commons and argue that free-market environmentalism will be much more effective in conserving nature.
Natural resources and property rights 
Critics point out that almost every patch of land on Earth was stolen (i.e. obtained through initiation of force) at some point in its history. The stolen land was later inherited or sold until it reached its present owners. Thus, property over land and natural resources is based on the initiation of force. Among those who make this argument, some claim that private property over natural resources is unique in being based on the initiation of force, while others hold that, by extension, private property over all goods derives from violence, because natural resources are required in the production of all goods.
Some supporters respond with the "water under the bridge" argument: transgressions of the past cannot all be rectified, and that an act of theft which happened long ago can reasonably be ignored. Critics argue that this implies that peaceful possession of property in the present legitimizes theft and/or trespass in the past. This requires a "cutoff" point: a point in time when illegitimate property becomes legitimate property. Some critics argue that any such point is arbitrary. Some supporters respond that property can only have a legal owner as long as there are no conflicting ownership claims to that property. The “cutoff” point, therefore, is when the owners whose property has been stolen drop their claim because property that has no ownership claims at all is free for anyone to homestead.
Many libertarians support the idea that only labor creates ownership (see the labor theory of property). Some hold the position that land and all natural resources are not man-made and therefore cannot be owned. Others believe the community is the owner and that people should pay rent to the community for land they use (see Georgism). The homestead principle allows land and other natural resources to be privately owned.
Political theorist Hillel Steiner emphasizes that all things made come from natural resources and that the validity of any rights to those made things depends on the validity of the rights to the natural resources. If land was stolen then anyone buying produce from that land would not be the legitimate owner of the goods. Also, if natural resources cannot be privately owned but are, and always will be, the property of all of mankind then NAP would be violated if such a resource would be used without everybody’s consent (see the Lockean proviso and free-market anarchism). Libertarian philosopher Roderick Long points out that, as natural resources are required not only for the production of goods but for the production of the human body as well, the very concept of self-ownership can only exist if the land itself is privately owned.
Sorites argument 
Consequentialist libertarian David Friedman argues against the natural law or first-principles interpretation of the non-aggression principle that ownership rights on body and property are absolute by using a Sorites argument. He begins by stating what he considers obvious: a neighbor aiming his flashlight at someone's property is not aggression, but that aiming at the same property with a gigawatt laser is. Yet both flashlight and laser shines photons onto the property, so there must be some cutoff point of how many photons one is permitted to shine upon a property before it is considered aggression. But the cutoff point can't be found by deduction alone, because of the Sorites paradox, so the non-aggression principle is necessarily ambiguous. Friedman points out the difficulty of undertaking any activity that has a certain amount of risk for others (i.e. flying) if the permission of thousands of people that might be affected by the activity is required. Many natural-rights libertarians, however, claim local law will regulate these issues without imposing on the absolute character of NAP.
Spectrum of aggression 
Some recent scholarship has questioned the traditional view of aggression as universally negative. It is claimed that, rather than concepts such as assertiveness, aggression, violence and criminal violence existing as distinct constructs that require different moral views, aggression exist instead along a continuum, with moderate levels of aggression being most adaptive for the individual, as well as for society as a whole.
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- J. C. Lester. "Why Libertarian Restitution Beats State-Retribution and State-Leniency (2005)". Retrieved 2011-11-12.
- Murray N. Rothbard. "Punishment and Proportionality (The Ethics of Liberty, 1982, Chapter 13)". Retrieved 2011-11-12.
- Philipp Bagus. "Can Dikes Be Private? : An Argument Against Public Goods Theory (Journal of Libertarian Studies, Vol. 20, No. 4, Fall 2006, pp. 21-40)". Retrieved 2011-11-17.
- Charles Murray, David Friedman, David Boaz, and R.W. Bradford. "Freedom: What’s Right vs What Works (Liberty Magazine, January 2005, Vol 15 No 1, pp. 31-39)". Retrieved 2011-11-15.
- Walter Block. "Jonah Goldberg and the Libertarian Axiom on Non-Aggression (LewRockwell.com, June 28, 2001)". Retrieved 2011-11-17.
- Murray N. Rothbard. "Libertarianism in Ancient China (Mises Daily, December 23, 2009)". Retrieved 2011-11-15.
- Epicurus. "The Internet Classics Archives: Principal Doctrines (translated by Robert Drew Hicks)". Retrieved 2011-11-15.
- G.A. Russell. The 'Arabick' interest of the natural philosophers in seventeenth-century England (Brill Publishers, 1994, ISBN 90-04-09459-8, pp. 224-239). Retrieved 2011-11-15.
- Samuel von Pufendorf. "On the Duty of Man and Citizen According to the Natural Law (Cambridge University, 1682, Book I, Chapter VI)". Retrieved 2011-11-15.
- John Lock. "Second Treatise of Civil Government (1690, 1764)". Retrieved 2011-11-15.
- Ayn Rand. "The Nature of Government (December 1963, from The Virtue of Selfishness, 1961, 1964)". Retrieved 2011-11-15.
- Ayn Rand. "The Roots of War (June 1966, excerpts)". Retrieved 2011-11-15.
- Ayn Rand. "Faith and Force: The Destroyers of the Modern World (1960, 1967, excerpts)". Retrieved 2011-11-15.
- Murray N. Rothbard. "War, Peace, and the State (April 1963)". Retrieved 2011-11-15.
- Murray N. Rothbard. "Introduction to Natural Law (The Ethics of Liberty, 1982, Chapters 1-5)". Retrieved 2011-11-16.
- Young Americans for Liberty. "I Pledge (YouTube.com, September 28, 2009)". Retrieved 2011-11-22.
- Henry Sturman. "Morality and Libertarianism (1999)". Retrieved 2011-11-17.
- Murray N. Rothbard. "Lifeboat Situations (The Ethics of Liberty, 1982, Chapter 20)". Retrieved 2011-11-15.
- Ben’s Blog. "Fred Phelps, Freedom of Speech and 'the Last Limits of the Endurable' (Ben’s Blog on Infinite Monkeys, Fri, 10/08/2010)". Retrieved 2011-11-26.
- Murray N. Rothbard. "Law, Property Rights, and Air Pollution (Cato Journal, Vol. 2, No. 1, Spring 1982, pp. 55-99)". Retrieved 2011-11-24.
- Graham Dawson. "Free Markets, Property Rights and Climate Change: How To Privatize Climate Policy (Libertarian Papers, Vol. 3, No. 10, 2011, pp. 1-29)". Retrieved 2011-12-04.
- Hillel Steiner. "Left-Libertarianism and the Ownership of Natural Resources (Bleeding Heart Libertarians, April 24, 2012)". Retrieved 2012-07-07.
- Eric Mack. "Natural Rights and Natural Stuff (Bleeding Heart Libertarians, April 23, 2012)". Retrieved 2012-07-07.
- Roderick Long. "Self-Ownership and External Property (Bleeding Heart Libertarians, April 25, 2012)". Retrieved 2012-07-07.
- David D. Friedman. "Problems (The Machinery of Freedom, 1989, Chapter 41)". Retrieved 2013-01-03.
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- The Ethics of Liberty e-book by Murray Rothbard, Mises.org
- A Theory of Socialism and Capitalism e-book by Hans-Hermann Hoppe, Mises.org
- The Non-Aggression Axiom of Libertarianism by Walter Block, LewRockwell.com
- Against Utilitarianism; or, Why Not Violate Rights if it'd Do Good by Tibor Machan, Mises.org
- Economics and Its Ethical Assumptions by Roderick Long, Mises.org
- New Rationalist Directions in Libertarian Rights Theory by N. Stephan Kinsella, Mises.org
- The Philosophy of Liberty, an animated production, derives a libertarian philosophy from the principle of self-ownership. Central to this is the non-aggression principle.
- Antiwar.com is a website devoted to opposing aggressive war, imperialism, and assaults on freedom associated with both. The editors describe their political view as libertarian.