Commas often play a crucial role in meaning. Even the directions for making hot cereal depend on the careful placement of a comma: Add Cream of Wheat slowly, stirring constantly. Here the comma tells the cook to add the cereal slowly. If the comma came before the word slowly, however, the cook might add the cereal all at once and stir slowly.
Because the comma can play many roles in a sentence, comma use often doesn’t follow hard and fast rules. Using commas effectively requires you to make decisions that involve audience, purpose, rhythm, and style—
Quick Help: Editing for commas
Using commas after introductory elements
Using commas in compound sentences
Using commas with nonrestrictive elements
Using commas to separate items in a series
Using commas with parenthetical and transitional expressions
Using commas with contrasting elements, interjections, direct address, and tag questions
Using commas with dates, addresses, titles, and numbers
Commas with quotations
Using commas for clarity
Avoiding unnecessary commas