Commas, FANBOYS

FANBOYS commas are those that must come before a coordinating conjunction (indicated by the acronym FANBOYS) when it joins two independent clauses—statements that could otherwise stand on their own as complete sentences:

• Alice drank tea, but the Dormouse slept.
• The March Hare dipped his watch into his tea, for he was altogether mad.
• The Walrus and the Carpenter invited the oysters on a walk, and the oysters came along, so the Walrus and the Carpenter ate them.

Note that joining independent clauses in this way requires both the comma and the conjunction; joining independent clauses with a comma alone is an error called a comma splice.

Also keep in mind that, while all coordinating conjunctions can join independent clauses, some of them—and, nor, but, or, yet—can also join words and phrases. In this situation, they only need a comma if they form a list:

• Yes: the Walrus and the Carpenter
• No: the Walrus, and the Carpenter
• Yes: the Walrus, the Carpenter, or the oysters

Compound Subjects and Predicates

These properties can also be combined. Remember that a clause is a subject–verb unit that can comprise multiple subjects and verbs (known as compound subjects and predicates). Take care not to insert commas within compound subjects and predicates unless creating a list of three or more items:

• No: Alice and the Hatter drank tea, and ate bread and butter, but the Dormouse slept, and snored.
   
  • While the coordinating conjunction between the two clauses ("but") requires a comma, both predicates—sets of verbs—are just two items joined by “and,” which does not require a comma.
     
• Yes: Alice and the Hatter drank tea and ate bread and butter, but the Dormouse slept and snored.
   
• Yes: Alice, the Hatter, and the March Hare drank tea, ate bread and butter, and were altogether mad, but the Dormouse simply closed his eyes, rolled over, and went back to sleep.
   
  • The compound subject is a list, which requires commas; both predicates are also lists of verbs and so require commas. The coordinating conjunction, "but," must also be preceded by a comma.

For more information on such constructions, see our page on serial commas.

Breaking down a sentence into grammatical units and making sure the commas are placed correctly can be tricky, but remember that, the more care you take with your writing, the less work readers will have to do to understand it. Incorrect comma usage can trip readers up, while correct comma usage will be nearly invisible, in the best possible sense.

More Information about FANBOYS Commas

• GWC FANBOYS Infographic
• GWC writing mechanics module: Commas
• Video (14:20): "Writing Skills: When to Use Commas with For, And, Nor, But, Or, Yet, So," JamesESL
• Handout (printable): "Commas vs. Semi-colons," Purdue OWL
• Exercises: "Commas with Coordinating Conjunctions," ProProfs
• Webpage: "Commas," University of North Carolina Chapel Hill
• Exercises: "Rearranging simple and compound sentences," Khan Academy