This study focuses on “the many careers of negative polarity items”, taking a diachronic perspective on NPIs in general and on scalar NPIs in particular. Its main thesis is that scalar NPIs are prototypical NPIs. The downward entailing contexts of NPIs can be explained and made cognitively accessible by the pragmatic mechanisms associated with scalar NPIs, viz. the capacity to evoke alternatives (ALT) and the scalar interpretation of these alternatives (SCALE). NPIs with standard contexts of distribution are, or are otherwise tied to, scalar expressions, while NPIs with an idiosyncratic range of contexts are not. The diachronic development of core NPIs crucially involves the loss, change or replacement of ALT and/or SCALE. Non-scalar elements can also become NPIs, but non-prototypical ones, viz. escort particles, analogy NPIs, or mimicry NPIs.