What is the Non-Aggression Principle? (NAP) A foundational principle of justice8 min read

The Non-Aggression Principle (NAP) is a foundational principle of justice. It’s a self-evident truth that we can use as a tool for determining violations of liberty. There is some disagreement between libertarian philosophers about the role NAP plays in the philosophy.

Libertarianism is a philosophy on the nature of civil governance, not simply one of many proposed political systems. So we can understand the role the NAP plays in libertarianism as being broadly applied, to include the polycentric legal orders in anarchist societies.

Below is a table showing how the NAP has been conceived in the past. This is not to say that the NAP per se has been around since the Epicureans. Rather, that the concept has been a self-evident hallmark of justice for centuries.

Simply stated, the NAP asserts that aggression is an illegitimate use of force. Immediately, this implies that there exists a legitimate use of force. This is not a pacifist rule. On-the-contrary, legitimate use of force can be (violent if necessary) to stop aggression, whatever that may be.

Let’s parse out some terms:

Aggression: The initiation of violence against a person or property, the threat of such force, or fraud.

Violence: physical force used to inflict injury or damage
Threat: oppression, coercion, menace
Fraud: Anything that is deceptive; this can include manipulation.

Illegitimate: unauthorized, unwarranted
Force: physical strength, power exerted against will or consent

The NAP more precisely stated:

The initiation of physical force used to inflict injury against a person or damage against property; the oppression, coercion, or menace of such; or use of deception or manipulation, is an unauthorized and unwarranted use of physical power, or power exerted against another’s will or consent.

So what is legitimate force?

Legitimate force is that which is used to stop aggression. This entails only a proportional response. To respond with a level of force beyond what is required to stop aggression is aggression itself.

Using the word ‘principle’ in the non-aggression principle is probably a misnomer, as it implies that it’s foundational. Instead, it’s axiomatic, or self-evident.

Resources & Further Reading

  1. https://wiki.mises.org/wiki/Principle_of_non-aggression
  2. http://bleedingheartlibertarians.com/2013/04/eudaimonism-and-non-aggression/


Formulated by


300’s BC


“Natural justice is a symbol or expression of usefulness, to prevent one person from harming or being harmed by another.”[4]


Abu Mansur Al MaturidiIbn Qayyim Al-JawziyyaAverroes

These Islamic theologians and philosopher wrote that man could rationally know that man had a right to life and property.

early 1200’s

Ibn Tufayl

In Hayy ibn Yaqzan 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 Tufayl influenced Locke’s notion of Tabula Rasa.[5]


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.”[6]


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.”[7]


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.”)


Mary Wollstonecraft

(“Vindication of the Rights of Men”) “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.”[8]


Thomas Jefferson

“Rightful liberty is unobstructed action according to our will within limits drawn around us by the equal rights of others. I do not add ‘within the limits of the law’, because law is often but the tyrant’s will, and always so when it violates the rights of the individual.” and “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)


Herbert Spencer

The law of equal freedom: “Every man is free to do that which he wills, provided he infringes not the equal freedom of any other man.” This notion of equal freedom goes back to earlier liberal thought.


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”.


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.”[9][10][11] Note that she stipulated the context – civilized society.


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[12]

L. Neil Smith

The libertarian science fiction writer claims, “No one has the right, under any circumstances, to initiate force against another human being, nor to delegate its initiation.” This is considered an imprecise formulation, since it explicitly ignores context.

Walter Block

“It shall be legal for anyone to do anything he wants, provided only that he not initiate (or threaten) violence against the person or legitimately owned property of another.”[13]

Kerry Baldwin |  

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