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 seeks to ground itself upon a natural law doctrine, but reaches some importantly different conclusions from Locke himself in several ways. Nozick appealed also to the Kantian idea that people should be treated as end in themselves (what he termed 'separatedness of persons'), not merely as a means to an end. Most controversially, and unlike Locke and Kant, Nozick argued that consistent application of self-ownership and non-aggression principle would allow and regard as valid consensual or non-coercive enslavement contracts between adults. He rejected the notion of inalienable rights advanced by Locke and most contemporary capitalist-oriented libertarian academics, writing in Anarchy, State, and Utopia that the typical notion of a "free system" would allow adults to voluntarily enter into non-coercive slave contracts. Epistemology In Philosophical Explanations (1981), which received the Phi Beta Kappa Society's Ralph 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 the Gettier problem 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 (S=Subject / P=Proposition): P is true S believes that P If it were the case that (not-P), S would not believe that P If it were the case that P, S would believe that P Nozick's third and fourth conditions are counterfactuals. He called this the "tracking theory" of knowledge. Nozick believed 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. Due to certain counterexamples that could otherwise be raised against these counterfactual conditions, Nozick specified that: If P weren't the case and S were to use M to arrive at a belief whether or not P, then S wouldn't believe, via M, that P. If P were the case and S were to use M to arrive at a belief whether