This article aims to better understand how Negative Polarity Items (NPIs) come into existence and how they change over time. It argues that an expression can become an NPI if its semantics makes it pragmatically useful in negative or downward entailing contexts, often because the meaning leads to pragmatic strength, but sometimes because its semantics leads to pragmatic attenuation. Special attention is given to two patterns involving pragmatic strength that can emerge historically: Negative Concord (NC) and what I call NPI Dualization. Both patterns, I argue, involve a pairing between an NPI that has an existential-like or low scalar semantics with a homophonous but semantically different expression with a freer distribution; the homophone is semantically negative in Negative Concord but semantically universal in NPI Dualization. The article argues that pragmatic strength plays an important role in the history of NPIs, both in their origin and in NPI Dualization, but is not directly relevant for their licensing synchronically. Instead, it argues for a return to the view that NPIs are lexically marked by a semantically meaningless distributional feature that needs to be valued syntactically. On a conceptual level, the article argues that historical shifts may be matters of likelihood.