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A '''scientific theory''' is a plausible and consistent explanation for observable [[phenomena]]. While a [[scientific law]] describes something that always happens in the same way, a scientific [[theory]] explains what causes it to do so.

A '''scientific theory''' is a plausible and consistent explanation for observable [[phenomena]]. While a [[scientific law]] describes something that always happens in the same way, a scientific [[theory]] explains what causes it to do so.

For example, doctors have long known that being near a person who has a communicable disease exposes you to a risk of catching it (see [[quarantine]]). It was a "law" of [[contagion]] that staying far away protected you from catching the disease, even before Pasteur's [[germ theory of disease]] provided the modern scientific explanation (the "theory").

For example, doctors have long known that being near a person who has a communicable disease exposes you to a risk of catching it (see [[quarantine]]). It was a "law" of contagion that staying far away protected you from catching the disease, even before [[Louis Pasteur|Pasteur]]'s [[germ theory of disease]] provided the modern scientific explanation (the "theory").

A successful theory is most consistent with the actual behavior of the universe.  When a phenomenon is discovered that is inconsistent with the prevailing theory, the theory is either revised or thrown out entirely.  An example of this is  [[Newtonian mechanics]]—while Newton's 3 laws of motion provide extremely accurate descriptions/predictions of the behavior of medium-sized objects at low speeds, they are inconsistent with the behavior of very large, very fast, or very small objects.  Newtonian mechanics has been shown to be a limiting case of the [[theory of relativity]] (in the limit where velocity goes to 0) and [[quantum mechanics]] (in the limit where [[Planck's constant]] goes to 0, essentially the limit of large objects).  Usually a theory which is inconsistent with some experimental evidence is not completely falsified; it is instead shown to be a simplified version of a more complete theory.

A successful theory is most consistent with the actual behavior of the universe.  When a phenomenon is discovered that is inconsistent with the prevailing theory, the theory is either revised or thrown out entirely.  An example of this is  [[Newtonian mechanics]]—while [[Isaac Newton|Newton]]'s 3 laws of motion provide extremely accurate descriptions/predictions of the behavior of medium-sized objects at low speeds, they are inconsistent with the behavior of very large, very fast, or very small objects.  Newtonian mechanics has been shown to be a limiting case of the [[theory of relativity]] (in the limit where velocity goes to 0) and [[quantum mechanics]] (in the limit where [[Planck's constant]] goes to 0, essentially the limit of large objects).  Usually a theory which is inconsistent with some experimental evidence is not completely falsified; it is instead shown to be a simplified version of a more complete theory.