When the series takes the form a, b, and c, a comma precedes the and.
- Confusing: The railroads in question are the New York Central, Pennsylvania and Chesapeake and Ohio. [The reader might surmise that the words Pennsylvania and Chesapeake and Ohio represent a single line or even three different lines.]
- Right: The railroads in question are the New York Central, Pennsylvania, and Chesapeake and Ohio.
- Confusing: For breakfast we had oatmeal, bacon, eggs and honey. [Omission of the comma after eggs suggests a mixture.]
- Right: For breakfast we had oatmeal, bacon, eggs, and honey.
[h.] A comma should follow an expression like he said which introduces a short quotation. (For longer or more formal quotations use a colon.)
- Right: He shouted, "Come on! I dare you!"
- Right: Our captain replied, "We're ready."
But for indirect quotations, a caution is necessary. Do not place a comma between a verb and a that or how clause which the verb introduces.
- Wrong: He explained, how the accident occurred.
- Right: He explained how the accident occurred.
- Wrong: The chauffeur told us, that the gasoline tank was empty.
- Right: The chauffeur told us that the gasoline tank was empty.
[i.] A comma is used to separate parts of a sentence which might erroneously be read together.
- Confusing: Long before she had received a letter.
- Better: Long before, she had received a letter.
- Confusing: We turned the corner and the horse stopped throwing us off.
- Better: We turned the corner and the horse stopped, throwing us off.
- Confusing: Through the alumni gathered there went a thrill of dismay.
- Better: Through the alumni gathered there, went a thrill of dismay.
- Wrong: For a dime you can buy two pieces of pie or cake and ice cream.
- Right: For a dime you can buy two pieces of pie, or cake and ice cream.
- Right: The man whom everybody had for years regarded as a crank and a weakling, is now praised for his sagacity and his strength.
- Right: In a situation so critical as to require the utmost coolness of mind, he lost his wits completely. [Here the confusion might not be serious if the comma were omitted, but separation of the long introduction from the main clause is desirable.]
[j.] Do not use superfluous commas:
1. To mark a trivial pause: