A Quick Guide to Using Commas

Generally speaking, the purpose of any punctuation is simply to note pauses in breathing and to clarify where ideas start and stop (Imagine if there was no punctuation or capitalization and all the words on a page were run together). This is only a partial list of the rules. The Longman Handbook has a chapter on this topic.

  1. A comma is placed before the conjunction (e.g. and, but, yet, etc.) if you have two "independent clauses" (meaning they could stand alone as complete sentences).

    2. Incorrect:

    The two men bolted the door but the intruder had already entered the window.

    Correct:

    The two men bolted the door, but the intruder had already entered the window.

    ("The two men bolted the door" could stand alone as a sentence and "The intruder had already entered the window" could stand alone as a complete sentence.)

  2. A comma is NOT placed before the conjunction (e.g. and, but, yet, etc.) if the clause following the main clause is not a complete sentence and cannot be omitted without altering the central idea of the sentence.

    3. Incorrect:

    I ran the race, but stumbled at the finish line.

    ("Stumbled at the finish line" is not in itself a complete sentence i.e. an "independent clause" and omitting it would alter the central idea of the sentence).

    Correct:

    I ran the race but stumbled at the finish line.

  3. According to the APA Publication Manual (newspapers use a different style manual and rule), a comma should separate a series of three or more elements (This is called "seriation").

    4. Incorrect:

    We have a choice of copper, silver and gold.

    Correct:

    We have a choice of copper, silver, and gold.

  4. Any sentence that starts with "If" or "Although" (called a dependent clause) should usually have a comma before the main clause (or main part of the sentence) begins.

    5. Incorrect:

    If you accept our conditions we shall agree to the proposal.

    Although he would have preferred to abstain Paul voted for the proposal.

    Correct:

    If you accept our conditions, we shall agree to the proposal.

    Although he would have preferred to abstain, Paul voted for the proposal.

  5. Any sentence that starts with a long "adverbial phrase" with "Because" or "After" usually has a comma before the main clause starts.

    6. Incorrect:

    After reading the paper the instructor turned pale.

    Because of the unusual circumstances the king sent his personal representative.

    Correct:

    After reading the paper, the instructor turned pale.

    Because of the unusual circumstances, the king sent his personal representative.

  6. Any sentence that starts with a very short "adverbial phrase" usually does not need a comma.

    7. Incorrect:

    After breakfast, the baroness mounted her horse.

    On Tuesday, he tried to see the mayor.

    Correct:

    After breakfast the baroness mounted her horse.

    On Tuesday he tried to see the mayor.

  7. A comma usually goes before a quotation that is a complete sentence and that begins with a capitalized word.

    8. Incorrect:

    Vera said calmly "I have no idea what you mean."

    The author stated "The effect disappeared within minutes" (Lopez, 1993, p.311).

    Correct:

    Vera said calmly, "I have no idea what you mean."

    The author stated, "The effect disappeared within minutes" (Lopez, 1993, p.311).

  8. A comma usually does not go before a quotation that is an integral part of the flow of the sentence. Usually the quotation does not start with a capitalized word and the word "that" rather than "stated" or "said" is used.

Incorrect:

Lopez found that, "the effect disappeared within minutes" (Lopez, 1993, p.311).

Correct:

Lopez found that "the effect disappeared within minutes" (Lopez, 1993, p.311).