 Negative polarity items (NPIs) like those highlighted in (17) are generally restricted to downward entailing or monotone decreasing contexts, those in which inferences from sets to subsets (but not vice versa) are valid (see Fauconnier 1975; Ladusaw 1980, 1996; Peters and Westerståhl 2006; and the  generalized quantifiers  entry). If I’ve eaten kumquats, I’ve eaten fruit, but not necessarily vice versa; this is an upward entailing (monotone increasing) environment. On the other hand, if I haven’t eaten fruit, I haven’t eaten kumquats, but not necessarily vice versa; this is a downward entailing (monotone decreasing)  environment.[10]  It is just in the latter case that NPIs are licensed.