Left-libertarianism is regarded by some as a doctrine that has a strong commitment to personal liberty and has an egalitarian view concerning natural resources, believing that it is illegitimate for anyone to claim private ownership of resources to the detriment of others. By this definition, left libertarians include anarcho-communists such as Kropotkin and anarcho-collectivists such as Bakunin. This type of left libertarianism is defended by contemporary theorists such as Peter Vallentyne, Hillel Steiner, and Michael Otsuka. Some left-libertarians of this type support some form of income redistribution on the grounds of a claim by each individual to be entitled to an equal share of natural resources. Noam Chomsky refers to himself as a left libertarian. The term is sometimes used synonymously with libertarian socialism or used in self-description by geoists.
Another definition of left-libertarianism or the libertarian left is defined by Roderick T. Long, as
... an integration, or I’d argue, a reintegration of libertarianism with concerns that are traditionally thought of as being concerns of the left. That includes concerns for worker empowerment, worry about plutocracy, concerns about feminism and various kinds of social equality.
This definition was originally popularized by some prominent members of the US libertarian movement, including Samuel Edward Konkin III and Roderick T. Long. Classically, "left" was used to denote opposition to the Ancien Régime. In the revolutionary French assemblies, some free-marketers such as Frederic Bastiat sat on the Left. According to Konkin, it was Murray Rothbard's idea to call his and Konkin's radical free-market libertarianism "Left," in order to appeal to the New Left and solidify an alliance with them and because they wanted to distinguish themselves as being interested in building counter-economic enterprises. In this view, libertarianism based on minarchism, gradualism, conservatism, or reformism is considered to be on the "Right. Left-libertarians of this type tend to support income redistribution to remedy past aggression, based on the entitlement theory of justice.
These two definitions are not totally compatible - those who accept one definition often reject the other. E.g. Few in the Alliance of the Libertarian Left would accept the first definition, while scholars such as David DeLeon would reject the second.
Left-libertarianism combines the libertarian premise that each person possesses a natural right of self-ownership with the egalitarian premise that natural resources should be shared equally. Left-libertarianism holds that unappropriated natural resources are either unowned or owned in common, believing that private appropriation is only legitimate if everyone can appropriate an equal amount, or if private appropriation is taxed to compensate those who are excluded from natural resources. This contrasts with right libertarians who argue for a right to appropriate unequal parts of the external world, such as land.
A number of Anglo-American political philosophers argue for the validity and necessity of some social welfare programs within the context of libertarian self-ownership theory. Peter Vallentyne and Hillel Steiner edited a primer, The Origins of Left-Libertarianism: An Anthology of Historical Writings. This text places Hugo Grotius, Thomas Jefferson, Thomas Spence, Thomas Paine, John Stuart Mill, Herbert Spencer and Henry George in the left libertarian tradition. Steiner himself wrote An Essay on Rights, a pioneering look at rights and justice from a left-libertarian perspective.
Philippe Van Parijs has written extensively on what he calls "real libertarianism", an approach very similar to Steiner and Otsuka's, and usually subsumed under the rubric of left-libertarianism. More recently, Michael Otsuka published Libertarianism Without Inequality, where he argues for incorporating egalitarian ideas into libertarian rights schemes.
Though not left-libertarians themselves, G. A. Cohen, John Roemer, and Jon Elster have also written extensively about the notions of self-ownership and equality, which provide the basis for this branch of left libertarian thought. This self-styled left-libertarianism's historical roots in the school of analytical Marxism has cast a cloud of doubt over it for both leftists and libertarians of more conventional stripe.
Pro-capitalist libertarian theory is sometimes called "right-libertarianism." It places a very strong emphasis on private property. Unrestricted capitalism and free markets are advocated by all right-libertarians, with some of them believing that property rights are the most basic rights of all, or that all genuine rights can be understood as property rights rooted in self-ownership (right-libertarians can and do differ on the notion of intellectual property). However, Vallentyne and some other left-libertarian philosophers take a more moderate – and, in their view, realistic - approach. They differ from mainstream right-libertarians on the issue that Robert Nozick calls the "original acquisition of holdings". That is the question of how property rights came about in the first place, and how property was originally acquired.
Right-libertarians hold that "wilderness" is unowned, and that unowned resources are made into property by use. This is generally referred to as homesteading. According to John Locke, when a person "mixes his labor" with a previously unowned object, it becomes his. A person who cultivates a field in the wilderness, by virtue of "mixing his personality" with the land, becomes the rightful owner of it (subject to the Lockean proviso that equally-good land remains free for the taking for others).
Vallentyne and some other left-libertarians hold that "wilderness" is commonly owned by all the people in a given area. Since there is no predetermined distribution of land and (they argue) since there is no reason to believe that, all things being equal, some people deserve more property than others, it makes sense to think of resources as commonly owned. Thus this brand of left-libertarianism denies that first use or "mixing labor" has any bearing on ownership. As such, it argues that any theory of left-libertarianism must structure its social and legal system around enforcing this idea of common ownership. Different proponents of this school of thought have different ideas about what can be done with property. Some believe that one must gain some kind of permission from their community in order to use resources. Others argue that people should be allowed to appropriate land in exchange for some kind of rent and they must either pay taxes on the profits made from the appropriated resources or allow the products of those resources to become common property.
Historically, the Georgists were a leftist tendency within libertarianism. They believed that all humanity rightfully owned all land in common and that individuals should pay rent to the rest of society for taking sole or exclusive use of that land. People in this movement were often referred to as "single taxers," since they believed that the only legitimate tax was land rent. However, they did believe that private property could be created by applying labor to natural resources.
Mutualism emerged from early 19th-century socialism, and is generally considered a market-oriented part of the libertarian socialist tradition. Mutualists generally accept property rights, but with a short abandonment time period. In other words, a person must make (more or less) continuous use of the item or else he loses ownership rights. This is usually referred to as "possession property" or "usufruct." Thus, in this usufruct system, absentee ownership is illegitimate, and workers own the machines they work with.
Mutualism has reemerged more recently, incorporating modern economic ideas such as marginal utility theory. Kevin A. Carson's book Studies in Mutualist Political Economy was influential in this regard, updating the labor theory of value with Austrian economics. Agorism, an anarchist tendency founded by Samuel Edward Konkin III, advocates counter-economics, working in untaxed black or grey markets, and boycotting as much as possible the unfree taxed market with the intended result that private voluntary institutions emerge and outcompete statist ones. Geoanarchism, an anarchist form of Henry George's philosophy, is considered left-libertarian because it assumes land to be initially owned in common, so that when land is privately appropriated the proprietor pays rent to the community. These philosophies share similar concerns and are collectively known as left-libertarianism.
In the seminal agorist work, The New Libertarian Manifesto, agorism is repeatedly described as left, presumably because it opposes the Old Order and is critical of political capitalism. Also, the agorist-inspired coalition Movement for the Libertarian Left and related groups use "left" in this manner.
Working with radicals like Ronald Radosh, Rothbard argued that the consensus view of American economic history, wherein government has stepped in as a countervailing interest to corporate predation, is fundamentally flawed. Rather, he argued, government intervention in the economy has largely benefited established players at the expense of marginalized groups, to the detriment of both liberty and equality. Moreover, the "Robber Baron Period", adulated by the right and despised by the left as a laissez-faire haven, was not laissez-faire at all but in fact a time of massive state privilege accorded to capital. Rothbard criticized the "frenzied nihilism" of left-libertarians but also criticized right-wing libertarians who were content to rely only on education to bring down the state; he believed that libertarians should adopt any non-immoral tactic available to them in order bring about liberty.
Rothbard's initial leftward impulse was maintained by Karl Hess, picked up by activists like Samuel Edward Konkin III (founder of the Movement of the Libertarian Left) and Roderick Long. These left-libertarians agree with Rothbard that presently-existing capitalism does not even vaguely resemble a free market, and that most presently-existing corporations are the beneficiaries and chief supporters of statism. By this line of reasoning, libertarianism should make common cause with the anti-corporate left. Rapprochement with the left has led many left-libertarians to reject some traditional right-libertarian stances, such as hostility to labor unions and support for intellectual property, or even to limit valid real-property rights to use-and-occupancy.