"You cannot say "no"."
Translation:Du kannst nicht "nein" sagen.
I would like to know the same thing. There is a general rule for placing "nicht" in a sentence. As I understand it, if you are negating a single word, nicht would come before that word. If you are negating the entire thought expressed by the sentence, nicht should come at the very end of the sentence except that the last position can be usurped by separable verb prefixes or verb infinitives "chased" by modal verbs or by a third thing that escapes me right now. By both of these "rules", "nicht sagen" seems right but DL disagrees.
"Kein" is an adjective meaning "not any" or "no," so literally, this would mean "You can't say any 'no,'" which is nonsense. You need to negate the verb "kannst," so use the adverb "nicht."
See this link about "kein" vs. "nicht": http://german.about.com/od/grammar/a/German-Negation.htm
There is no consistency with the placement of "nicht" among the answers to these questions. Können Sie uns nicht explizit sagen? Warum muss es so uneindeutig sein? Das ist so lächerlich! Ich hasse diese zweideutigen Antworten! Sei präzise, Duo! Erklär alle deine Antworten! Keiner sollte kostenlos arbeiten! Es ist nicht unser Arbeit!
No; the verb "kannst" is not in imperative form. If we try to put in imperative form, though, the sentence ends up kind of strange (something like "Don't be able to say 'no.'").
Actually, I'm not sure that modal verbs even have imperative forms--according to my source ( http://www.canoo.net/inflection/k%C3%B6nnen:V:haben), "können" doesn't seem to. Hypothetically, though, the imperative form would be the stem of the verb, so we end up with "Könn nicht 'nein' sagen." ("Don't be able to say 'no.'").
If you just want to say "Don't say 'no,'" use "Sag nicht 'nein.'"
This is how I understand the placement of nicht. Correct me if I'm wrong.
Du kannst "nein" nicht sagen. --> nicht negates sagen
- Translate: You can not say anything, including nein.
Du kannst nicht "nein" sagen. --> nicht negates "nein"
- Translate: You can say things, but cannot say nein in particular.