In linguistics, a polarity item is a lexical item that can appear only in environments associated with a particular grammatical polarity – affirmative or negative. A polarity item that appears in affirmative (positive) contexts is called a positive polarity item (PPI), and one that appears in negative contexts is a negative polarity item (NPI).
The environment in which a polarity item is permitted to appear is called a "licensing context". In the simplest case, an affirmative statement provides a licensing context for a PPI, while negation provides a licensing context for an NPI. However, there are many complications, and not all polarity items of a given type need necessarily have exactly the same set of licensing contexts.