Use commas with coordinating conjunctions that join two independent clauses. There are seven coordinating conjunctions: for, and, but, or, yet, and so. Using the acronym FANBOYS will help you remember them.
For a definition and examples of independent and dependent clauses, see Chapter 12, Lesson 1.
You should only connect two independent clauses per sentence. Long strings of independent clauses are usually considered run-on sentences.
Example 1 - Tell me what you eat, and I will tell you what you are.
The coordinating conjunction “and” is connecting two independent clauses. Notice that in the first clause, the subject is a missing but implied “you.” We still consider clauses with an implied “you” (what we term imperative statements) to be independent.
Example 2 - I looked all over the house, but I couldn’t find my keys.
The coordinating conjunction “but” is connecting two independent clauses. Since the subject “I” is restated in the second clause, we consider it a separate subject.
Example 3 - Ms. Brenner went to the local police station and disputed her speeding ticket with the officer at the front desk.
Notice that the coordinating conjunction “and” is connecting two verbs (“went” and “disputed”) instead of two independent clauses. Do not use commas when connecting two verbs, adjectives, or nouns unless you want to place special emphasis on the second item.
Use the comma to separate three or more elements in a series. Although you are not absolutely required to place a comma before the last item in a series, it seems to be a general academic convention to include. Whether you decide to use it or not, make sure to keep it consistent throughout your writing.
Example 1 - During her trip to Europe, Erica visited Sweden, Norway, Denmark, and Holland.
Use a comma after a dependent clause when it comes before an independent clause. Use a comma with a dependent clause that comes after an independent clause only if the subordinating conjunction implies contrast (i.e. though, whereas).
Example 1 - If you speak the truth, have a foot in the stirrup.
The subordinating conjunction “if” marks the dependent clause as coming before the independent clause. Place a comma between the ending of the dependent clause and the beginning of the independent clause.
Example 2 - He cancelled his magazine subscription because he thought the editors no longer addressed important issues.
The subordinating conjunction “because” does not imply a contrast between the independent clause and the dependent clause. Therefore, we do not use a comma before “because.”
Example 3 - Allen is scrambling to finish all of his projects, whereas Amy planned ahead and had everything finished by last Thursday.
The subordinating conjunction “whereas” implies a contrast between the independent clause and the dependent clause.
Many sentences begin with a prepositional, gerund, or infinitive phrase that introduces or explains the sentence. Place a comma between the end of the introductory phrase and the beginning of the subject. If the introductory phrase is less than four words long, you often do not need to use a comma, although it is never wrong to use one to be safe.
For definitions and examples of phrases, see Chapter 12, Lesson 2.
Example 1 - To get a good grade, you must complete all of your assignments.
The sentence is introduced with an infinitive phrase, and the comma is placed before the subject “you.”
Example 2 - Justifying a fault doubles it.
Notice that the gerund phrase is not working as an introductory phrase, but as the subject itself. If a phrase is filling the role of sentence subject, then we do not place a comma after it.
For each example sentence, insert missing commas or omit incorrectly placed commas.
- I finally found my keys and I got to work just in time.
- Mrs. Contreras threw out her old coffee table, and cleaned the carpet.
- Taking the elevator to the roof we hoped we could see the skyline, and the bay.
- Though Susan wasn’t feel well she went to the store anyway and bought ice cream pizza, and candy.
- I let my neighbor borrow my phone, because she said hers was tapped by the police.