Usage of '吗' in questions
你好！ I have noticed that when Duolingo gives questions to translate, 吗 is only used half the time. Are there certain situations or types of questions where it is not needed? 谢谢！
If the sentence already contains a question word, such as 什么 (what?), 怎么 (how?), 谁 (who?) etc., then 吗 is not necessary. Even with those words, some people do add 吗 for emphasis, but there is debate among grammarians about whether or not this is technically incorrect.
Even with those words, some people do add 吗 for emphasis, but there is debate among grammarians about whether or not this is technically incorrect.
You must have misunderstood something… Nuance exists:
- 你是谁？Who are you?
- 你是谁吗？Are you someone? You're someone?
- 那里有什么？What's there?
- 那里有什么吗？Is something there? There's something?
Right, but in your particular examples the meaning of the question word changes and is no longer a question word. It rather becomes an unspecific noun. Another example would be:
哪里都有好吃的东西吗？ (Are there are delicious things to eat everywhere?)
What I was referring to were cases when people still add 吗 with a question word for extra emphasis. Examples:
你什么时候要去吗？(What time do you want to go?)
你怎么还没睡醒吗？(How have you still not woken up?)
These kinds of sentences are where the grammar debate lies. Some grammarians say that standard Chinese doesn't allow for this kind of thing while others say that it can. Apparently other dialects do allow for this double-question construction which is why it creeps into Mandarin in certain parts of China.
Okay, so the grammarians you mentioned were talking about the evolution of Mandarin — but I don't see such sentences become mainstream. Update: (?) Maybe we are not talking about the same thing. See my another reply.
I didn't acquire a particular dialect because I learned Mandarin at school. To me, 你什么时候要去吗 is taking 什么时候 as “at an unspecified time”, not “at what time”. And 你怎么还没睡醒吗 sounds like “你怎么(了)？还没睡醒吗？”. Besides, 哪里(w/o 都)有好吃的东西吗 means “Anywhere I can find delicious food?”
Once you have gained enough experience of (near) standard Mandarin, you can easily notice whether people are speaking with their local accent. So I never worried about it and I would allow some loss of precision when parsing their dialect.
I still don't understand what the “extra emphasis” you mean for your examples. Is the speaker trying to confirm something? If so I think my translation is more precise, thus not a dialectal matter.