A period marks the end of a statement. No other mark will do.
Some writers want to pause between statements, using a comma. Don’t do that. Today’s readers want a complete stop at the end of one statement before going to the next. Really. (You just read a one-word sentence, which is perfectly acceptable.)
Using a comma to join two independent clauses is a mistake called a “comma splice.” For example, Jack fell down the hill, Jill fell down from laughing. We want a period, not a comma, because we have two distinct statements.
In the above example, you might join the two statements with a semicolon, forming what is called a “compound sentence.” However, today’s audience has little use for semicolons. They would rather see separate statements using periods.
We might use a comma and a conjunction to join Jack’s and Jill’s independent, yet related, actions. Jack fell down the hill, and Jill fell down laughing. The coordinate conjunction says the two actions are related and justifies the pause with a comma instead of a hard stop with a period.
