or not P, then S would believe, via M, that P. Where M stands for the method by which S came to arrive at a belief whether or not P. A major criticism of Nozick's theory of knowledge is his rejection of the principle of deductive closure. This principle states that if S knows X and S knows that X implies Y, then S knows Y. Nozick's truth tracking conditions do not allow for the principle of deductive closure. Nozick believes that the truth tracking conditions are more fundamental to human intuition than the principle of deductive closure. Later books The Examined Life (1989), pitched to a broader public, explores love, death, faith, reality, and the meaning of life. According to Stephen Metcalf, Nozick expresses serious misgivings about capitalist libertarianism, going so far as to reject much of the foundations of the theory on the grounds that personal freedom can sometimes only be fully actualized via a collectivist politics and that wealth is at times justly redistributed via taxation to protect the freedom of the many from the potential tyranny of an overly selfish and powerful few. Nozick suggests that citizens who are opposed to wealth redistribution which fund programs they object to, should be able to opt out by supporting alternative government approved charities with an added 5% surcharge. However, Jeff Riggenbach has noted that in an interview conducted in July 2001, he stated that he had never stopped self-identifying as a libertarian. Roderick Long reported that in his last book, Invariances, "[Nozick] identified voluntary cooperation as the 'core principle' of ethics, maintaining that the duty not to interfere with another person's 'domain of choice' is '[a]ll that any society should (coercively) demand'; higher levels of ethics, involving positive benevolence, represent instead a 'personal ideal' that should be left to 'a person's own individual choice and development.' And that certainly sounds like an attempt to embrace libertarianism all over again. My own view is that Nozick's thinking about these matters evolved over time and that what he wrote at any given time was an accurate reflection of what he was thinking at that time." Furthermore, Julian Sanchez reported that "Nozick always thought of himself as a libertarian in a broad sense, right up to his final days, even as his views became somewhat less 'hardcore.'" The Nature of Rationality (1993) presents a theory of practical reason that attempts to