Keep or keeps

It isn't singular and plural exactly. It's the infinitive in the first sentence, and the third person singular in the second.
In the first sentence the main verb is does, with a secondary verb keep. In the second sentence Everyone is treated as singular, so the verb keeps is third person singular.

Thanks. So it basically depends on the construction of the sentence. Words can function differently. Would that be correct?

Yes.

I just got a confused because 'everyone' is considered singular so I thought that what follows has to be singular but it did not sound right. I guess I would have to go with what sounds right!

So even if a previous word is singular, the word that follow is not necessarily singular, and it depends on the context. Would that be correct?

Thanks again.

Most nouns form the plural by adding an S, for example one dog, two dogs. Verbs work differently. The present tense of most verbs goes like this:
I keep.
You keep.
He/she/it keeps.
We keep.
They keep.
Everyone is singular, so it works like he/she/it, and is followed by keeps

Yes, thanks. In general in works like he/she/it, but this was not the case in the first example where it was an infinitive. Right?

I am not sure what infinitive is but thanks for pointing this out.

Everyone works like he/she/it.
The infinitive is the base form of the verb, usually expressed as to keep.
If you have two verbs working together in a sentence, the first is usually in the normal form, like the example I gave earlier, and the second verb is usually either the infinitive (which may include the to, or not), or the

Thanks. Do you mean the example you gave based on the sentence I wrote (In the first sentence the main verb is does, with a secondary verb keep)?

Yes. Exactly.

Great. I have one last question.

Would it have been correct if I said: you mean the example you gave based on the sentence I had written (instead of I wrote).