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I left out rules about commas and letter writing, addresses, dates, and direct quotations/ dialogue. If you really want those rules leave a comment and I'll write them up for next week.
Use a comma to set off a noun of direct address:
Sophia, take my hand.
It’s a date, Stella.
She’s not worth it, Bobby, walk away.
Use a comma to set off introductory words:
Yes, you may stay.
Use a comma to set off interrupters in a sentence:
He has, however, never called me.
This flower bed, by the way, needs to be weeded.
Use a comma to set off words or phrases in a series. Use a comma before and unless the items go together (bread and butter, salt and pepper):
She made a bouquet with lilies, irises, and tulips.
Last week he hiked the hill, swam the river, and took a nap.
Please put the butter, the jam, and the salt and pepper on the table.
Use a comma to make a sentence clear:
When painting in the day light is critical.
When painting in the day, light is critical
Use a comma between two or more descriptive adjectives Do not place a comma between the last adjective and the noun or pronoun:
The sleek, silver car slid to a stop.
If the adjective is a color or a limiting adjective, no comma is used:
The yellow floppy hat hung on a hook.
Use a comma to set off an appositive:
Dr. Gordon, the town vet, asked me on a date.
My favorite animal is Nutmeg, the alpaca by the tree.
Use a comma to set off a title following a name:
Bill Gordon, D.V.M., came to the rescue.
Use a comma before a dependent clause at the beginning of a sentence:
After I went boating, I took a bath.
If the dependent clause is at the end of a sentence, no comma is needed:
We went to dinner after we went to the beach.
Use a comma before the conjunction that joins two independent clauses (compound sentences)
We had fun at the beach, but we returned home exhausted.
Use a comma after two introductory prepositional phrases or after a long prepositional phrase when the subject follows it:
Outside the door on the deck, Sophia bathed in the cast iron tub.
Behind a canvas curtain, she felt secluded.
Use a comma after an introductory participial phrase.
Slipping on the edge, Ryan fell in with a splash.
Use a comma to set of adjectives in apposition:
Long and lingering, the kiss left her breathless.
The kiss, long and lingering, left her breathless.
(a big thank you to Wanda C. Phillips, Ed.D., who's book Easy Grammar: Plus has been used by our homeschooling family for many years)