Memo 3-2

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Rule 1 – conjunctions

Use a comma to divide two main clauses joined by a coordinating conjunction: and, or, nor, for, so, but, yet.

Test for correct usage: Each clause is independent (a main clause.)

*Note: The comma can be optional if the first clause has five or fewer words.

Examples: I have painted the entire house, but he is still working on sanding the doors.

*I painted and he sanded the doors.

Rule 2 – introductory phrases (dependent clause)

Place a comma after introductory elements including introductory phrases, dependent clauses, and introductory transitional words (see 2a below).

Test for correct usage: What follows the comma is an independent (main) clause.

*Note: The comma can be optional if the introductory phrase has three or fewer words.

Examples: To apply for this job, you must have previous experience.

If you are not sure about this, let me know now. *In February many couples give each other candy or flowers.

Rule 2a – introductory word

Use a comma when beginning sentences with an introductory transitional word or words such as nevertheless, actually, furthermore, yes, in addition, etc.

Examples: Yes, I do need that report. Nevertheless, we have to make a decision soon.

Rule 3 – items in a series

Use a comma to divide all items in a series. Be sure to use a comma before the conjunction preceding the last item in a series.

Example: The trip includes overnight stays in San Diego, Santa Fe, and Phoenix.

I want to thank my parents, Oprah, and Bill.*

*Note: Omitting the comma before the conjunction can cause miscommunication, e.g. thanking two people: …my parents, Oprah and Bill vs. thanking four people: …my parents, Oprah, and Bill.

Rule 4 – adjacent adjectives (modifying the same noun)

Use a comma to separate adjacent adjectives that modify the same noun.

Test for correct usage: The adjectives can be divided with “and” or reversed without changing the meaning.

Examples: He is a strong, healthy man. We stayed at an exclusive, expensive summer resort.

Rule 5 – nonessential (additional or contrasting elements) or interrupting information

Use commas to divide nonessential, or interrupting, sentence elements from essential sentence elements, including words such as therefore and however when they are used as interrupters.

Test for correct usage: Remove the nonessential element; you should still have an independent (main) clause.

Examples: I am, as you have probably noticed, very nervous about this.

Let’s use red for the company logo, not blue. I would be happy, however, to volunteer for the Red Cross.

Rule 6 – dates (month/day/year)

Insert commas before and after the year when the month, day, and year are given (in this sequence). *Exception: Don’t use a comma with a partial date (month/year; month/day) or a date written in day-month-year format.

Examples: We hired a new CEO on December 5, 2017, from Germany.

*They met in December 2015 in Mill Valley.

*They met on December 5 in Mill Valley.

Rule 7 – elements of an address

Use commas to divide elements of any address. Place commas before and after the last element, except when a ZIP code is the last element.

Exception: Don’t include a comma after the state when the two-letter capitalized abbreviation is used.

Examples: I lived at 2812 Ivy Avenue, San Francisco, California, for 20 years. My address is 2812 Ivy Avenue, San Francisco, CA 94105.

I lived in San Francisco, CA for 20 years.

Rule 8 – clarification/direct address/full-sentence direct quotation

Use commas where they are needed for clarification.

Test for correct usage: Remove the clarification element; you should still have an independent (main) clause.

Examples: Will you, Aisha, do that assignment for me? Sam, we must take action this week.

The speaker remarked, “I have never expected to see so many changes.”

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