later the theory of quantum mechanics (established in 1925), each one more accurate than the last. A major challenge to this model came from the work of the historian and philosopher Thomas Kuhn (1922–1996) in his work The Structure of Scientific Revolutions published in 1962. Kuhn, a former physicist, argued against the view that scientific progress was linear, and that modern scientific theories were necessarily just more accurate versions of theories of the past. Rather, Kuhn's version of scientific development consisted of dominant structures of thought and practices, which he called "paradigms", in which research went through phases of "normal" science ("puzzle solving") and "revolutionary" science (testing out new theories based on new assumptions, brought on by uncertainty and crisis in existing theories). In Kuhn's model, different paradigms represented entirely different and incommensurate assumptions about the universe. The mode was thus uncertain about whether paradigms shifted in a way which necessarily relied upon greater attainment of truth. In Kuhn's view, Aristotle's physics, Newton's classical mechanics, and Einstein's Relativity were entirely different ways to think about the world; each successive paradigm defined what questions could be asked about the world and (perhaps arbitrarily) discarded aspects of the previous paradigm which no longer seemed applicable or important. Kuhn claimed that far from merely building on the previous theory's accomplishments, each new paradigm essentially throws out the old way of looking at the universe, and comes up with its own vocabulary to describe it and its own guidelines for expanding knowledge within the new paradigm. Kuhn's model met with much suspicion from scientists, historians, and philosophers. Some scientists felt that Kuhn went too far in divorcing scientific progress from truth; many historians felt that his argument was too codified for something as polyvariant and historically contingent as scientific change; and many philosophers felt that the argument did not go far enough. The furthest extreme of such reasoning was put forth by the philosopher Paul Feyerabend (1924–1994), who argued that there were no consistent methodologies used by all scientists at all times which allowed certain forms of inquiry to be labeled "scientific" in a way which made them different from any other form of inquiry, such as witchcraft. Feyerabend argued harshly against the notion that falsification was ever truly followed in the history of science, and noted that scientists had long undertaken practices to arbitrarily consider theories to be accurate even if they failed