Use commas to separate items in a series.

• Example: My culture is not the same as Salvadorian, Cuban, or Guatemalan.

The comma before and is called the Oxford comma (or serial comma) and is optional. However, if you don’t use it, you can sometimes cause confusion.

• Example: I’d like to thank my parents, Bob and Marcy. (With one interpretation, the parents’ names are Bob and Marcy. With the other interpretation, "my parents," "Bob," and "Marcy" are all different people.)

Do NOT use a comma before the first or after the last item in a series:

• Example: The food culture in Mexico and Italy shows Ø similar foods, ingredients, and special occasions Ø that connect these two counties together.

Use a comma before coordinating conjunctions when these words connect two independent clauses. Use the mnemonic word FANBOYS (for, and, nor, but, or, yet, so) to remember all the coordinating conjunctions.

• Example: I love sports very much, but I had an injury.

Do NOT use a comma before coordinating conjunctions when these words connect words or phrases (instead of full independent clauses).

• Example: I like sports Ø but not very much.

Use a comma after an introductory transition word such as however, still, furthermore, and moreover.

• Example: Thus, full hybrids are fuel-efficient and environmentally friendly.

Use a comma to separate an introductory dependent phrase or clause from the independent clause.

• Example: Before “highwheel safeties” were invented, only men were seen riding bicycles.
• Example: Holding a camera on the way to the top of the rock, she monitored their climb.

Do NOT use a comma when a dependent clause beginning with an adverb (such as while, since, because) FOLLOWS an independent clause.

• Example: My family has used different methods around the house to save water Ø because my parents know how expensive the water bill can get.

Do NOT use a comma between a subject and its verb or between a verb and its complement.

• Example: Holding a camera on the way to the top of the rock Ø is more challenging.
• Example: One of the two conducted experiments Ø showed that high exposure to sexual material on TV puts virgins at a higher risk. 

Use commas to set off non-essential phrases and clauses (sometimes called non-restrictive phrases and clauses) which disrupt the normal flow of the sentence by providing extra information.

• Example: Chaadev, who spoke out against the regime, was punished. (The non-essential phrase “who spoke out against the regime” is an added detail about Chaadev which isn’t necessary information to identify Chaadev.)
• Example: The report from the European Commission shows that the only official language of France is French, which is an unfamiliar language to me. (The non-essential phrase “which is an unfamiliar language to me” is an added detail about French which isn’t necessary information to identify what French is.)
• Example: Craigslist is noted for its full-scale information that people are looking for such as housing, jobs, services, and pets, which are based in San Francisco. (The non-essential phrase “which are based in San Francisco” applies to the entire list, and only relative clauses that are non-essential/non-restrictive can describe a clause (see this flowchart for more information). Without this comma, the reader would think that only the pets are based in San Francisco.)
• Example: This is a journal report for Chief Learning Officer, a publication for people who want to improve their leadership and management skills. (The non-essential phrase “a publication for people…” gives extra information about the Chief Learning Officer. It is a reduced form of the phase “which is a publication for people….” See the Relative Clause chapter for more information on reduced relative clauses.)

Do NOT use commas for essential (restrictive) phrases and clauses that are key to the meaning of the sentence.

• Example: The intellectuals Ø who spoke out against the regime Ø were punished. (The essential phrase “who spoke out against the regime” provides crucial information about who these intellectuals are.)

Use commas to set off parenthetical and transitional expressions, contrasting elements, interjections, and tag questions.

• Example: Engelstein, on the other hand, uses information about the Geographical Society and free economic associations.
• Example: Cepeda brings forth the fact that, yes, the majority of Latinos in America are of Mexican decent.
• Example: All types of bikes can cause problems, not just the beach cruiser.

Use commas to shift between your words and a quotation. This is similar to the use of interrupting elements mentioned above.

• Example: “Thanks to the Internet,” he said, “I do not have to go outside to the cinema on such a freezing day.”

Use a comma to introduce a quotation with an introductory dependent phrase (see rule above) or following a reporting verb such as says, believes, and argues.

• Example: Long-Solis and Vargas claim, “Many people restrict their diet as a form of penitence at this time of year” (146).

Do NOT use a comma when you lead into a quote without a reporting verb.

• Example: Long-Solis and Vargas describe how Ø “many people restrict their diet as a form of penitence at this time of year” (146).

Use a comma to separate items in dates and addresses.

• Example: On January 1st, 2015, I started work at 1 Shields Avenue, Davis, California.

Use a comma to separate two adjectives if they could be joined by and.

• Example: I grew up learning history from giant, old textbooks from high school.

Use a semicolon to link two independent clauses NOT joined with a coordinating conjunction (FANBOYS).

• Example: Food is all around the world; it is a symbol that joins countries together.

The purpose is to subtly show the relation between two clauses (rather than using a period or a comma + coordinating conjunction) if the relationship between the two clauses is clear.

You can still use a conjunctive adverb or transitional expression after a semicolon (therefore, however, in fact, for example) in order to clarify the relationship between the two independent clauses, but don’t forget to use a comma after this word/phrase.

• Example: While I was sleeping, my muscles were at rest; however, my mind was awake.

Use a semicolon to separate items in a series containing other punctuation.

• Example: To propel the car, the series hybrid uses an electric motor charged by a gasoline engine; the parallel hybrid uses both an electric motor and a gasoline engine; a mild hybrid uses a fuel engine assisted by an electric motor; and a full hybrid can use an electric motor, combustion engine, or both of them.

Use a semicolon to separate two or more sources in a single parenthetical reference.

• Example: (Ricento, 2006; Spolsky, 2004)