A. Correct Usage

1. 1. Use a comma to separate dependent and independent clauses.

   Do you remember the dependent clauses? If not, here’s a small recap.

   • a. Relative clauses
     • a) which, who, when, where [only]
   • b. Introductory clauses
     • a) Prepositional
     • b) Modifier
     • c) Subordinating conjunctions
     • d) Appositives
   • c. Non-essential clauses
   • d. Participial/modifying clauses

   If you need to remember any of these topics, please refer to lessons 2.0 and 3.0 for more details.

   Whenever we have a dependent clause, it MUST be separated from the independent clause using a comma.

   Example:

   In May 1942, Congress instituted the Women’s Auxiliary Army Corps, later upgraded to the Women’s Army Corps, which had full military status.

   Show Explanation

   This example has 3 dependent clauses, and all are separated using commas.

   Let’s break this down:

   • The idea in blue is an introductory clause beginning with a preposition. Notice how we add a comma to separate the introductory clause from the independent clause.
   • The idea in green is a modifier; notice how we add a comma to separate the modifier from the independent clause.
   • The final idea in purple is a relative clause 'which'; notice how that's separated from the modifying dependent clause.

   Example 2:

   During World War II, some 350,000 women served in the U.S. Armed Forces, both at home and abroad.

   Show Explanation

   Notice that the underlined portion of the sentence is an introductory clause, separated from the independent clause with a comma.

   Example 3:

   They included the Women’s Airforce Service Pilots, who, on March 10, 2010, were awarded the prestigious Congressional Gold Medal.

   Show Explanation

   In this example, we placed a double comma before and after the 'who' phrase, making it non-essential. Non-essential means the information is not needed to understand who or what the sentence is discussing.

   Example 4:

   Between 1940 and 1945, the female percentage of the U.S. workforce increased from 27 percent to nearly 37 percent, and by 1945 nearly one out of every four married women worked outside the home.

   Show Explanation

   In this example, the dependent prepositional introductory clause is separated from the independent clause with a comma.

   In sum, commas are used to separate a dependent clause from both the independent clause and other dependent clauses.

2. 2. We add a comma to a series or list.

   This will also be covered under the 'parallelism' chapter. However, our focus now is a series of items or a list.

   Example:

   My best friend celebrated my birthday by surprising me with gifts, feeding me cake, and taking me out to dinner.

   Show Explanation

   The underlined portion is a series of items, a.k.a. a list, separated by commas, and at the end of the list is a 'comma and.'

   The 'comma and' at the end of the list is called the Oxford comma. In most American-based writing, the Oxford comma is used.

   Both using and omitting the Oxford comma can be correct, but be consistent in your usage.

   However, what if you get two answers like this:

   1. No change
   2. with gifts, feeding me cake and taking me out to dinner.
   3. with gifts, feeding me cake, and taking me out to dinner.

   Which one would you choose?

   Show Explanation

   We know both B and C are grammatically correct. But the better answer is with the 'comma and' - answer C.

   The 'comma and' is better than the 'no comma and' in lists. Remember this!

3. 3. Commas are used between interchangeable adjectives.

   This is a good rule since many international students need clarification when a comma is placed between two adjectives.

   To do so, the two adjectives MUST be interchangeable. What does that mean? That means we can switch the places of the two adjectives without changing the sentence's meaning.

   Example:

   He was a strong, healthy man.

   He was a healthy, strong man.

   Show Explanation

   The two examples above show that if two adjectives are interchangeable, we could place a comma between them.

   How would you know? By using the word 'and' between the two. If you can place the word 'and' between the two adjectives, then you can use a comma between them.

   Example: He was a strong and healthy man.

   Incorrect Example:

   We stayed at an expensive summer resort.

   We cannot say:

   • We stayed at a summer expensive resort.
   • We stayed at an expensive and summer resort.

   Therefore, a comma is NOT acceptable between these two adjectives.

4. 4. A comma is used with FANBOYS when the two ideas are independent.

   FANBOYS stands for For, And, Nor, But, Or, Yet, So.

   Example:

   Between 1940 and 1945, the female percentage of the U.S. workforce increased from 27 percent to nearly 37 percent, and by 1945 nearly one out of every four married women worked outside the home.

   Show Explanation

   The comma with the FANBOYS 'and' combines two independent clauses:

   • First independent clause
   • Second independent clause

5. 5. Use a comma between city and state.

   You're not directly tested on this rule; however, it's useful to know.

   Example:

   I went to Cairo, Egypt.

   Show Explanation

   In context, seeing this might confuse as to the functions of commas.

   Example:

   I went to Cairo, Egypt, during the day.

   If you didn't know that a comma is used between a city and a state, then you might assume this is a comma fragment—a comma between the verb and direct object.

B. Sentence Formulas

Sometimes, it's easier to remember rules if you remember the formulas for the rules. So here's a list of 'sentence' formulas for commas.