I have looked up 誰 in the dictionary, and found that both

  * 誰も
  * 誰でも

can mean everyone and everybody.

If there is a difference between them, what is the correct way to use each of
them?

It is not limited to 誰, I also want to consider other question words such as,
何、どこ、いつ、どちら、どれ、etc.
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2016-03-05T04:07:42.307
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2016-03-07T04:41:27.530
2016-03-05T04:23:26.983
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question
grammar word-choice polarity-items
How to use ～でも and ～も?
It's difficult to explain but I'm going to write up examples.

  * みんな金ない、俺も、お前も、誰もない: Everyone lacks money, me either, you either, anyone either. 
  * あなたにやるものは、たとえあなたが誰でも、ない: I have nothing to give you, whoever you are.
  * 私は私以外の誰でもない: I am none other than me.
  * 中に誰もいない: there is nobody inside
  * そんなにありがたい人は、たとえあなたが誰でも、いない: you can't have such a precious person, whoever you are.
  * 誰も良い (awkward, "everyone is good" translates to みんな良い)
  * 誰でも良い: I'd appreciate whoever. 
  * 誰も思う (誰もが、誰しも、誰しもが are more common for "everyone thinks")
  * その立場なら、誰でもそう思う: Everyone would think so, if he was in that position.
  * 誰も思うな: don't think of anyone / everyone, don't think!
  * 誰も優しくするな: everyone, don't be kind to him/her.
  * 誰にも優しくするな don't be kind to anyone.
  * 誰でも優しくするな: don't be kind to everyone.
  * 来たのが誰でも戸を開けるな: don't open the door, whoever the visitor is.
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2016-03-06T09:45:27.543
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2016-03-06T12:50:08.367
2016-03-06T12:50:08.367
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answer
でも is translated as "even" and も is translated as "also" commonly.

For example, 彼でも英語が話せる(Even he can speak English.) and 彼も英語が話せる(He can also
speak English.)

In the case of 誰. 誰も means "all" like 彼の生徒は、誰も英語が話せる(All his students can
speak English) and 彼の生徒は誰も英語が話せない(All his students are incapable of speaking
English -> None of his students can speak English.)

誰でも means "anybody" and "whoever".
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2016-03-06T11:52:23.357
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2016-03-07T04:41:27.530
2016-03-07T04:41:27.530
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answer