They are not really synonyms i guess. Even though both means "why", they are used in different contexts. " wieso" is used if you are asking about something that is done intentionally. >> E.g. wieso rennst du? (Why are you running? You feel like he is doing exercise) But on the other hand, if you are questioning about something unintentional, then you use "warum". >>E.g. warum rennst du? (Sometime suddenly started running. You have no clue) (Someone please correct me if i missed something.)
Here are some links to a source which shows many uses of kein/keine and nicht:
Sorry! I am learning too. What is your first language? Here are some resources:
http://www.germanlanguageguide.com/german/grammar/ http://german.about.com/od/gamesexercises/u/PracticePerfect.htm#s2 http://coerll.utexas.edu/gg/gr/mis_04.html http://en.wikipedia.org/wiki/German_sentence_structure#Adverbial_clauses http://www.vistawide.com/german/grammar/german_cases_nominative.htm http://en.pons.eu/translate?q=kann&l=deen&in=&lf=de http://www.germandictionary.org/browse/letter/c/page-2 http://dict.tu-chemnitz.de/doc/about.en.html http://www.dartmouth.edu/~german/Grammatik/WordOrder/WordOrder.html http://yourdailygerman.wordpress.com/tag/difference-between-sondern-and-aber/ http://www.canoo.net/services/OnlineGrammar/Satz/Negation/Stellung/nichtkontrast.html?lang=en
Well, "Why can't we be friends?" is from a song and that would use "können", but the question above is "Why aren't we friends?" Certainly, "Why shouldn't we be friends?" could have been used in the song and that would have used "darfen", but it just wasn't used in the song. "can't" or "cannot" leaves the impression that you just want to know the reasons why you are unable to be friends. "shouldn't" means that you can but some reasons would make it unfavorable to be friends. There are a lot of things people shouldn't do that they do, but when they can't do something, there is something that must be changed to be able to do that. In the song the emphasis is placed on "Why can't WE BE FRIENDS?" to imply that nothing should prevent us, we should overcome any obstacle. When "shouldn't is used the emphasis is usually placed on "shouldn't" and you also imply that we should be friends. When children ask "Why CAN'T we be friends?" they are unhappy that they cannot and wish they could be friends, but it does not imply that they are going to overcome the obstacle, just that they might think it is unfair.