Law (in science)
High school
A scientific law is a statement, often an equation, that describes a pattern that holds in every tested case, without explaining why.
Examples
Examples
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Newton’s law of universal gravitation, $F = G m_1 m_2 / r^2$
High school
Newton’s law of gravitation is a law because it is an equation that describes how strongly masses attract. It is not a theory, because it does not explain why masses attract; general relativity, a theory, does.
Non-examples
Things that may be mistaken for examples.
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Before an experiment: “Bean plants grow taller with more hours of light each day”
Elementary
“Bean plants grow taller with more hours of light” is a hypothesis, because it is a prediction that an experiment can test and could show to be false. It is not a theory or a law, because no body of evidence supports it yet, and it is not a conjecture, because experiments, not proofs, decide it.
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The theory of evolution by natural selection
High school
Evolution by natural selection is a theory, because it explains a broad range of observations (fossils, genetics, the distribution of species) and is supported by a large body of evidence. It is not a law because it explains why species change rather than describing one pattern. It is not a hypothesis because it has be demonstrated via experiments.
Properties
- A law describes what happens, and a theory explains why. A theory does not become a law by gaining more evidence.
Distinctions involving this term
- Conjecture vs. hypothesis vs. law vs. theory: A conjecture is a statement believed true but not yet proved, and it belongs to mathematics, where statements are settled by proof. In science, where statements are tested by evidence, a hypothesis is a testable proposal, and a theory is a well-supported explanation of many observations. A law describes a pattern that holds in every tested case, often as an equation such as $F = G m_1 m_2 / r^2$, without explaining why the pattern holds; explaining it is the job of a theory. In everyday speech, “theory” means a guess, but in science a theory is an a principle or body of principles that explains observed data and phenomenon.