Among the uses of ουκουν (oukoun) Denniston (1954: 235) mentions 'ουκουν ου, ουκουν ... ου, expecting a negative answer.' This paper argues that Denniston's view, which is shared by most (all?) other grammars and dictionaries of Ancient Greek (e.g.Kühner-Gerth 2, 164: 'Wenn nach ουκουν eine verneinende Antwort erwartet wird, so wird demselben die Negation ου nachgesetzt', Smyth § 2651 a: 'ουκουν ου expects the answer no', Liddell-Scott-Jones s.v. ουκουν) should be rejected. Actually, the answer is never no. As always, ουκουν expects an a irmative answer, in this case to a negated question: 'Is it not true, then, that not X?' = 'Surely, then, not X?' To be sure, ου does occur as an answer, but this can be shown to be a proposition (or sentence) negative (= not), rather than an answering particle like no. The situation in Greek is compared with negatives in several other languages, notably Latin and Old French. Finally, Modern Greek is briefly discussed, which, unlike Ancient Greek, does have a negative answering particle, viz. οχι, alongside a proposition negative, viz. δε(ν).