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. A thesis claims that "social ties are deeply interconnected with vital parts of Nozick's later philosophy", citing these two works as a development of The Examined Life. 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. Utilitarianism Nozick created the thought experiment of the "utility monster" to show that average utilitarianism could lead to a situation where the needs of the vast majority were sacrificed for one individual. He also wrote a version of what was essentially a previously known thought experiment, the experience machine, in an attempt to show 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 a machine-induced experience of a wonderful life over real life? Nozick says no, then asks whether we have reasons not to plug into the machine and concludes that since we desire to be really impressed by things and not just feel something pleasurable, it does not seem to be rational to plug in, hence ethical hedonism must be false. Philosophical method Nozick was notable for the exploratory style of his philosophizing and for his 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). Invariances In his 2001 work, Invariances, Nozick introduces his theory of truth, in which he leans towards a deflationary theory of truth, but argues that objectivity arises through being invariant under various transformations. For instance, space-time is a significant objective fact because an interval involving both temporal and spatial separation is invariant, whereas no simpler interval involving only temporal or only spatial separation is invariant under Lorentz transformations. Nozick argues that invariances, and hence objectivity itself, emerged through a theory of evolutionary cosmology across possible worlds. Bibliography Anarchy, State, and Utopia (1974) Philosophical Explanations (1981) The Examined Life (1989) The Nature of Rationality (1993/1995) Socratic Puzzles (1997) Invariances: