When do we use a comma before or? Confusion usually surrounds comma usage. Coordinating conjunctions usually play a role in this perplexing area. The word “or” is no exception.
Sometimes a comma precedes “or” and sometimes it does not. Deciphering when to employ a comma helps improve the clarity of your writing. To break this conjunction “code” you need to understand the difference between independent and dependent clauses.
When to Use a Comma Before Or
Independent vs Dependent Clauses
Simply put an independent clause represents a finished thought. It operates as a simple sentence with a subject and a verb. In a complex sentence, an independent clause works in tandem with another clause: dependent or independent.
In contrast, a dependent clause cannot function as a simple sentence. It labors as a modifier for an independent clause. In essence, a dependent clause is a word group that provides extra detail in a sentence.
Coordinating conjunctions and “or”:
“Or” is one of seven coordinating conjunctions that join two clauses. You can easily memorize these seven coordinating conjunctions with the mnemonic FANBOYS. Each letter stands for one of these words: “for”, “and”, “nor”, “but”, “or”, “yet” and “so” .
You use a comma when any of the coordinating conjunctions precede an independent clause. In contrast, you do not need a comma before the conjunction to join a dependent clause.
Each coordinating conjunction serves a purpose. “Or” introduces choice into a sentence. It combines two grammatical elements of equivalent weight.
Independent Clauses Need a Comma Before Or
Strong concise statements develop when you place a comma before “or”. Using a comma to join two independent clauses makes a sentence easier to read.
- Mary may choose to buy a dog, or she may choose to purchase a llama.
You can reduce both clauses to simple sentences by removing the coordinating conjunction “or”. Try separating the clauses to see if they express a complete thought.
- Mary may choose to buy a dog.
- She may choose to purchase a llama.
If the coordinating conjunction joins two simple sentences a comma must precede it.
No Comma Before a Dependent Clause
Conjunction connecting a dependent clause requires no punctuation.
- Mary may choose to buy a dog or a llama.
Without a subject and a verb, the second clause cannot stand alone as a simple sentence. Hence, the second clause follows the conjunction and becomes dependent on the first clause.
Comma Before “Or” In A List
In a list with two items never add a comma before or. The second item in the list will operate as a dependent clause. If “or” treads on the heels of a dependent clause no comma heralds the conjunction.
- Would you like water or milk?
In this example, water coordinates with milk. This coordination makes the comma unnecessary.
When a list consists of three or more items you have a choice to make. You may add a comma before “or” or not. The serial comma is a hotly debated topic.
The serial comma often goes by another name: the Oxford comma. The comma gets its name from the Oxford University Press that regularly employs its use. Fans of the serial comma argue that a comma before “or” makes a sentence easier to read. This is true in a sentence with plenty of coordinating items.
- Do you want a red, white, or black crayon?
- Do you want a red, white or black crayon?
Both examples above are correct. Some writers use the serial comma while others do not. This comma is a stylistic choice.