Like let's say,
"if someone happen(s) to remember, please remind me..."
"if someone go(es) there, please tell me..."
Note: I am NOT a grammar teacher. In fact, I rather fail at explaining grammar even though I can do it. :V
You can't give an accurate summary of it. It depends on which one sounds more smooth. Say it out loud if that helps you hear the difference. But next time, call them plural verbs as that would make more sense and be easier to decipher.
Someone/Everyone/Anyone/Nobody are a little tougher to decipher than most normal words. Usually if there is more than one subject, you would use a plural verb (and this may confuse you) that DOES NOT in fact include "s".
"He talks on the phone." (singular)
"They talk on the phone." (plural)
See: http: //data.grammarbook.com/blog/verbs/when-to-add-s-to-a-verb/ (get rid of space between http: and //)
But that isn't the main question.
The problem is, there are differences. Like:
"Everyone stands up when the teacher comes in."
"Everyone should stand up when the teacher comes in."
This ties in with present and past tense, which affects how you would write things. By statements and questions, do you mean in conversation or in, say, writing? They have differences.