many sets of tests. Feyerabend argued that a pluralistic methodology should be undertaken for the investigation of knowledge, and noted that many forms of knowledge which were previously thought to be "non-scientific" were later accepted as a valid part of the scientific canon. Many other theories of scientific change have been proposed over the years with various changes of emphasis and implications. In general, though, most float somewhere between these three models for change in scientific theory, the connection between theory and truth, and the nature of scientific progress. The nature of scientific discovery Individual ideas and accomplishments are among the most famous aspects of science, both internally and in larger society. Breakthrough figures like Sir Isaac Newton or Albert Einstein are often celebrated as geniuses and heroes of science. Popularizers of science, including the news media and scientific biographers, contribute to this phenomenon. But many scientific historians emphasize the collective aspects of scientific discovery, and de-emphasize the importance of the "Eureka!" moment. A detailed look at the history of science often reveals that the minds of great thinkers were primed with the results of previous efforts, and often arrive on the scene to find a crisis of one kind or another. For example, Einstein did not consider the physics of motion and gravitation in isolation. His major accomplishments solved a problem which had come to a head in the field only in recent years — empirical data showing that the speed of light was inexplicably constant, no matter the apparent speed of the observer. (See Michelson–Morley experiment.) Without this information, it is very unlikely that Einstein would have conceived of anything like relativity. The question of who should get credit for any given discovery is often a source of some controversy. There are many priority disputes, in which multiple individuals or teams have competing claims over who discovered something first. Multiple simultaneous discovery is actually a surprisingly common phenomenon, perhaps largely explained by the idea that previous contributions (including the emergence of contradictions between existing theories, or unexpected empirical results) make a certain concept ready for discovery. Simple priority disputes are often a matter of documenting when certain experiments were performed, or when certain ideas were first articulated to colleagues or recorded in a fixed medium. Many times the question of exactly which event should qualify as the moment of discovery is difficult to answer. One of the most