Punctuation: Commas Are Our Friends 170 The Least You Need to Know · Punctuation helps convey the meaning of your sentences to your readers. · Between sentences, the most common mark of punctuation is the period; within sentences, the most com- mon mark is the comma. · Semicolons separate complete sentences; colons introduce lists. · Hyphens separate word parts; dashes separate sentence parts or sentences. · Godzilla is frightening; punctuation isn't.