811. Use commas to set off clauses or phrases that add merely a descriptive idea to the expression modified.
Abraham Lincoln, who was born in a log cabin, became one of the greatest presidents.
They, reading the newspaper, did not hear me come in.
812. Use commas between adjectives in a series if the position of the adjectives can be logically interchanged.
Each one carried a red, white, and blue flag.
813. Use commas between words, phrases, or clauses in a series.
He sent me two books, a drum, and a small wagon.
Seeing the dark sky, feeling the sharp wind, and knowing that my family would be worried, I hurried home.
If he had not been ill, if the bank had not failed, and if my credit had not been exhausted, you would never have found me here.
814. Use a comma before the and connecting the last two members of a series.