Dear Grammar Guru,
When do I use a comma with and?
Use a comma before and:
(1) in a series of three or more words, phrases, or clauses
Many artists, writers, and composers find inspiration in daydreaming and mediation. Today many authorities omit the comma before and if the phrases are short. Caution: Make sure the sentence does not confuse the reader if the comma is omitted. Example: I enjoy reading, writing and walking dogs. Writing dogs? How does one do that? Retain the final comma, or rewrite the sentence: I enjoy reading novels, writing poetry and walking dogs.
(2) after the first sentence in a compound sentence
A compound sentence is two sentences joined by a coordinating conjunction (most commonly and, but, or). Example: Henry David Thoreau urged simple and honest approaches to life, and he was jailed for refusing to pay a tax to support the Mexican War. Notice there is a complete sentence on both sides of and.
Do not a comma after and unless another rule dictates that usage. Example: "I did not ask you to finance the project, and, in my opinion, you are out of line," my sister said. The comma after and is not because of and. In my opinion is a parenthetical expression or interrupter; it requires a comma before and after it. Without the parenthetical expression, the sentence would require no comma after and. "I did not ask you to finance the project, and you are out of line," my sister said.