The word theory is perhaps the most misunderstood word in science. In everyday usage, the synonym of theory is guess or hunch. Yet according to the National Academy of Sciences (2008: 11), "The formal scientific definition of theory is quite different from the everyday meaning of the word. It refers to a comprehensive explanation of some aspect of nature that is supported by a vast body of evidence." A theory, then, is an explanation rather than a guess. Many high school (and even, unfortunately, some college) textbooks describe theories as tested hypotheses, as if a hypothesis that is confirmed is somehow promoted to a theory, and a really, really good theory gets crowned as a law. But rather than being inferior to facts and laws, a scientific theory incorporates "facts, laws, inferences, and tested hypotheses" (National Academy of Sciences 1998: 7). Theories explain laws! To explain something scientifically requires an interconnected combination of laws, tested hypotheses, and other theories.
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