Robert Nozick (November 16, 1938 – January 23, 2002) was an American philosopher and professor at Harvard University. He was educated at Columbia (A.B. 1959, summa cum laude), where he studied with Sidney Morgenbesser, at Princeton (Ph.D. 1963), and Oxford as a Fulbright Scholar. He was a prominent American political philosopher in the 1970s and 1980s. He did additional but less influential work in such subjects as decision theory and epistemology. His Anarchy, State, and Utopia (1974) was a libertarian answer to John Rawls's A Theory of Justice, published in 1971. He was born in Brooklyn, the son of a Jewish entrepreneur from Russia, and married the American poet Gjertrud Schnackenberg. Nozick died in 2002 after a prolonged struggle with cancer. His remains are interred at Mount Auburn Cemetery in Cambridge, Massachusetts.

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Nozick was Joseph Pellegrino University Professor at Harvard University.

Nozick's Anarchy, State, and Utopia (1974), which received a National Book Award, argues among other things that a distribution of goods is just if brought about by free exchange among consenting adults and from a just starting position, even if large inequalities subsequently emerge from the process. Nozick appealed to the Kantian idea that people should be treated as ends (what he termed 'separateness of persons'), not merely as a means to some other end. Nozick here challenges the partial conclusion of John Rawls's Second Principle of Justice of his A Theory of Justice, that "social and economic inequalities are to be arranged so that they are to be of greatest benefit to the least-advantaged members of society."

Anarchy, State and Utopia claims a heritage from John Locke's Second Treatise on Government and tries to base itself upon a natural law doctrine. Locke only relied on natural law as God given to counteract the King of England's claim to divine right and thus claim to all the property of England. Nozick suggested, again as a critique of utilitarianism, that the sacrosanctity of life made property rights non-negotiable. This principle has served as a foundation for many libertarian pitches into modern politics.

Nozick retreated from some of the views he expressed in Anarchy, State, and Utopia in one of his later books, The Examined Life, calling those views "seriously inadequate." In a 2001 interview, however, he clarified his position: "What I was really saying in The Examined Life was that I was no longer as hardcore a libertarian as I had been before. But the rumors of my deviation from libertarianism were much exaggerated."

In Philosophical Explanations (1981), which received the Phi Beta Kappa Society's Waldo Emerson Award, Nozick provided novel accounts of knowledge, free will, personal identity, the nature of value, and the meaning of life. He also put forward an epistemological system which attempted to deal with both Edmund Gettier-style problems and those posed by skepticism. This highly influential argument eschewed justification as a necessary requirement for knowledge.

Nozick's Four Conditions for S's knowing that P were:

(1) P is true

(2) S believes that P

(3) If it were the case that (not-P), S would not believe that P

(4) If it were the case that P, S would believe that P

Nozick's third and fourth conditions are counterfactuals. Nozick calls his theory the 'tracking theory' of knowledge. Nozick believes that the counterfactual conditionals bring out an important aspect of our intuitive grasp of knowledge: For any given fact, the believer's method must reliably track the truth despite varying relevant conditions. In this way, Nozick's theory is similar to reliabilism.

The Examined Life (1989), pitched to a broader public, explores love, death, faith, reality, and the meaning of life. The Nature of Rationality (1993) presents a theory of practical reason that attempts to embellish notoriously spartan classical decision theory. Socratic Puzzles (1997) is a collection of papers that range in topic from Ayn Rand and Austrian economics to animal rights, while his last production, Invariances (2001) applies insights from physics and biology to questions of objectivity in such areas as the nature of necessity and moral value.

He created the thought experiment of the "utility monster" in order to show that average utilitarianism could lead to a situation where the needs of the vast majority were sacrificed for one individual. Along with that, he came up with the thought experiment of The Experience Machine where he showed that ethical hedonism was false. Nozick asked us to imagine that "superduper neuropsychologists" have figured out a way to stimulate a person's brain to induce pleasurable experiences. We would not be able to tell that these experiences were not real. He asks us, if we were given the choice, would we choose the machine over real life? Nozick then asks whether or not we have reasons not to plug into the machine and concludes that since it does not seem to be irrational to plug in, ethical hedonism must be false.

Nozick was notable for his curious exploratory style and methodological ecumenism. Often content to raise tantalizing philosophical possibilities and then leave judgment to the reader, Nozick was also notable for drawing from literature outside of philosophy (e.g., economics, physics, evolutionary biology).

Robert Nozick argued that a consistently libertarian society would allow and regard as valid consensual/non-coercive enslavement contracts between adults, rejecting the notion of inalienable rights. He wrote in Anarchy, State and Utopia:

 

• Invariances: The Structure of the Objective World (2001/2003) ISBN 0-674-01245-3
• Socratic Puzzles (1997) ISBN 0-674-81653-6
• The Nature of Rationality (1993/1995) ISBN 0-691-02096-5
• The Examined Life (1989) ISBN 0-671-72501-7
• Philosophical Explanations (1981) ISBN 0-19-824672-2
• Anarchy, State, and Utopia (1974) ISBN 0-631-19780-X