誰も used in a positive sentence

Question

I am reviewing the interrogative words like 何、誰、どこ etc. and I saw 誰も being used in a positive sentence, I wonder what the difference would be if みんな were used instead. For example:

誰もが知っている

みんなが知っている

Some people said it means the same but if there are two words it's not for nothing and there must be some nuance.

Also, if 誰も can be used in a positive sentence to mean everyone, that means どこも, 何も can also be used in a positive sentence?

I came to think that the particle も after the interrogative word doesn't mean no-, but it's rather a sort of group meaning like "every", for example:

誰もが知っている = everyone knows 誰もが知らない = everyone does not know

Is it right? Then what is the nuance? Can someone explain it in detail?

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One more question, I also review the particles behind the interrogative words, and I think I understood how it worked, can you tell me if the following examples are correct please

• 誰にも任せない = I leave it to nobody.
• 誰にでも任せないで = Don't leave it to anybody.
• 誰でもができる = Anybody can do it.
• 誰もがしらない = Nobody knows.
• 誰かがいるの = Is there someone?

Another question, is the particle が obligatory in order to make these sentences correct grammatically? Often I see 誰でも being used without が.

Answer 1

Since most of Japanese Question + も patterns ("any- (... not)") are, as you know, only allowed to be used with negative predicates, we usually make some workarounds to express the "every-" idea. Unfortunately, the ways we've taken are not consistent across words, so maybe you're confused by it.

          any- (+ NEG)  no matter - (regular)     every- (irregular)
誰        誰も          誰でも                    誰も (noun), 誰もかも (noun)
何        何も          何{なん}でも                   何もかも (noun)
いつ      いつも{HLL}        いつでも                  (いつも can be used)
どこ      どこも        どこでも                  どこも{HLL}全部 (noun), どこも{HLL}
どれ      どれも        どれでも                  (どれも can be used)
どう      どうも        どうでも                  (does it exists?)

In other words, we ordinarily reword "every-" using "no matter -" series as long as possible, and avoid using words in the "every-" row unless when they're really needed.
(-も and -でも can attach to every noun + case combinations (e.g. 誰からも, どこへでも, どれに関しても). These extended expressions stand for both "any-" in negative and "every-" in positive.)

Back to your questions:

Some people said it means the same but if there are two words it's not for nothing and there must be some nuance.

The nominalized 誰も and みんな has exactly the same meaning, but if compared, 誰も has stronger nuance than みんな, because みんな literally means "the entire people".

Also, if 誰も can be used in a positive sentence to mean everyone, that means どこも, 何も can also be used in a positive sentence?

As you can see from my table above, there's no 何も which means "everything", you have to use 何もかも. どこも can be used without changing its form, but mind the accent.

誰もが知っている = everyone knows 誰もが知らない = everyone does not know

Theoretically 誰もが知らない could mean "everyone does not know" (for Japanese grammar doesn't prohibit it), but practically it only means "no one knows".

• 誰にも任せない = I leave it to nobody.
• 誰にでも任せないで = Don't leave it to anybody.
• 誰でもができる = Anybody can do it.
• 誰もがしらない = Nobody knows.
• 誰かがいるの = Is there someone?

You're almost correct, but 誰にでも任せないで is "don't leave it to-no-matter-who" → "don't leave it to everyone". One thing else is that 誰かがいるの doesn't completely equal to 誰かいるの. The former is unlikely to be uttered when the speaker speaks toward the assumed "someone".

Often I see 誰でも being used without が.

Yes, -でも + が is possible, at least for 誰でも, 何でも and どれでも, but it's redundant. I don't see any change in meaning.