A condition which must hold for a result to be true, but which does not guarantee it to be true. If a condition is both necessary and sufficient, then the result is said to be true iff the condition holds.
Necessary
See also
SufficientExplore with Wolfram|Alpha
References
Jeffreys, H. and Jeffreys, B. S. "Necessary: Sufficient." §1.036 in Methods of Mathematical Physics, 3rd ed. Cambridge, England: Cambridge University Press, pp. 10-11, 1988.Referenced on Wolfram|Alpha
NecessaryCite this as:
Weisstein, Eric W. "Necessary." From MathWorld--A Wolfram Web Resource. https://mathworld.wolfram.com/Necessary.html