# Special case

## Specific, usually well-known application of a mathematical rule or law / From Wikipedia, the free encyclopedia

In logic, especially as applied in mathematics, concept A is a **special case** or **specialization** of concept B precisely if every instance of A is also an instance of B but not vice versa, or equivalently, if B is a generalization of A.^{[1]} A limiting case is a type of special case which is arrived at by taking some aspect of the concept to the extreme of what is permitted in the general case. If B is true, one can immediately deduce that A is true as well, and if B is false, A can also be immediately deduced to be false. A degenerate case is a special case which is in some way qualitatively different from almost all of the cases allowed.