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{{merge|counter-example}}
{{merge|counter-example}}
A '''counterexample''' is an example that is opposite to a theory or argument.
A '''counterexample''' is an example that is opposite to a theory or argument.
==In Science and Logic==
For example, the well-proven theory that cigarettes cause [[lung cancer]] has the '''counterexample''' of the (rare) individual who might smoke his entire life and not develop lung cancer. The counterexample does not disprove the theory.
For example, the well-proven theory that cigarettes cause [[lung cancer]] has the '''counterexample''' of the (rare) individual who might smoke his entire life and not develop lung cancer. The counterexample does not disprove the theory.
A theory of universality, such as the claim that ''all'' species [[theory of evolution|evolved]], can be disproved by just one '''counterexample''', such as a species (like the [[whale]]) that lacks a plausible evolutionary path.
A theory of universality, such as the claim that ''all'' species [[theory of evolution|evolved]], can be disproved by just one '''counterexample''', such as a species (like the [[whale]]) that lacks a plausible evolutionary path.
[[category:logic]]
[[category:logic]]
==In Mathematics==
The word counter-example originated in mathematics. It means an example that contradicts a general statement; therefore, the single example proves the statement false. Consider the statement
"Every number ending in the digit 7 is prime." 7, 17, 37, 47, 57, and 67 are all prime, but 27 is not, so 27 is a counterexample.