This note presents a simple, novel diagnostic for determining the phrase structural status of negative markers cross-linguistically, a topic of enduring interest (for recent approaches and references see Haegeman; Zanuttini; Giannakidou, Landscape and Polarity). If the sentential negative marker in a given language is phrasal (an XP, generally adverbial), it will occur in the collocation why not?; if it is a head (an X 0, generally clitic-like), it will not. In the latter languages, the word for ‘no’ can sometimes be (...) used, itself (presumably) a phrasal negative adverb. (A fortiori, languages with possibly word-internal morphological markers for sentential negation, such as Turkish, will not allow these markers in the collocation.) The first group of languages, those with XP negative markers, is given in 1: (1) a. English why not? * why no?1 b. German warum nicht? * warum nein? c. Dutch waarom niet? * waarom nee? d. Danish hvorfor ikke? * hvorfor nej? e. Icelandic hverfor ekki? * hvarfor nej? f. French pourquoi pas? * pourquoi non?2 g. Tsez shida anu? * shida ey? The second class of languages, those with X0 negative markers, is given in 2. (shrink)