Punctuation marks are used for the following: to create pauses, flow, or rhythm within a sentence or a text. The way to do this is to use commas or periods to create pauses, commas or conjunctions to create flow, commas or colons to create rhythm, etc. However, one thing that punctuation cannot do is affect verb agreement. Verb agreement means that the subject and the predicate (verb) are in the same number: if the subject is singular, the verb will also be singular; if the subject is plural, so is the verb. This depends on the subject, not on punctuation.
