How to use comma?

1. Use a comma before any coordinating conjunction (and, but, for, or, nor, so, yet) that links two independent clauses.

Example: "I went running, and I saw a duck."

You may need to learn a few grammatical terms to understand this one.

An independent clause is a unit of grammatical organization that includes both a subject and verb and can stand on its own as a sentence. In the previous example, "I went running" and "I saw a duck" are both independent clauses, and "and" is the coordinating conjunction that connects them. Consequently, we insert a comma.

If we were to eliminate the second "I" from that example, the second clause would lack a subject, making it not a clause at all. In that case, it would no longer need a comma: "I went running and saw a duck."

2. Use a comma after a dependent clause that starts a sentence.

Example: "When I went running, I saw a duck."

A dependent clause is a grammatical unit that contains both subject and verb but cannot stand on its own, like "When I went running ..."

Commas always follow these clauses at the start of a sentence. If a dependent clause ends the sentence, however, it no longer requires a comma. Only use a comma to separate a dependent clause at the end of a sentence for added emphasis, usually when negation occurs.