What exactly happens when you embed a clause with も?

Question

I understand what's going on when you embed a interrogative clause using か、like when you form pronouns like 誰か、or write things like 「ええ、何を食べたか知らないよ・・・。」

However, It's still beyond me what も、does when used to embed a clause; I get how 誰か means 'somebody' or 'whom', but I don't understand why what's normally the temporally inclusive topic marking particle makes it's 誰も mean 'everyone' or 'anyone', which is what I'm hoping to learn.

Edit: Could you also explain how the meaning changes when using でも instead of using も？

Answer 1

Words like 誰も and 何も etc. when used with negative verbs take on their negative counterpart essentially.

誰かいた　Someone was there.

誰もいなかった　No one was there. (There wasn't anyone there)

For the most part the でも just sort of emphasizes it in a the sense:

それは有名でもない　That is not even famous.

It's actually just the same particle も attached to the particle で (or also the copula だ in て form)