Should you use a comma before or? The answer depends on how you are using or. Always place a comma before or when it begins an independent clause, but if it begins a dependent clause, don’t. In a series (or list) of three or more items, you can use a comma before or, but this is a preference, not a rule.
People often get muddled about whether to place a comma before conjunctions like and, so, because, and or. Or is a coordinating conjunction, which means that it coordinates two elements of equal syntactic importance (i.e., two things of identical grammatical weight).
Commas before “Or” in Lists
When just two short grammatical elements are coordinated with or, do not separate them with a comma.
You may want to use a comma in a series of three or more things. This is the much-debated Oxford comma (or serial comma). Although the Oxford University Press uses it (hence the name), American English writers use it more often than British English writers. Whether or not you should use it is a stylistic choice. For example, both of these examples can be considered correct:
We can invest our savings in stocks, bonds, or real estate.
When each element separated by or is just one or two words, the reader will have little trouble mentally sorting things out with whichever style you choose.
That said, advocates of the Oxford comma do have a strong argument when it comes to the clarity. Consider the longer series of coordinating items in this sentence; within the series itself, there is a phrase with a necessary or.
Notify your doctor if you experience dizziness, fainting spells, nausea, vomiting, weak or rapid pulse, or difficulty breathing.
Including the final comma in this sentence makes it much more readable. It eliminates a mental “hoop” for the reader to jump through. What’s more, it has a much cleaner typographical appearance.
Commas before “Or” When Beginning an Independent Clause
It is considered good style to place a comma before or when it begins an independent clause. An independent clause is a clause which could stand alone as its own sentence, because it has its own subject and verb.
Each of the two clauses here can stand independently. This is why there should be a comma before or.
She may go on a luxury vacation.
If the clause beginning with or were rewritten to eliminate the subject and verb, it would not be able to stand on its own, and there would be no comma.
Want to learn more about commas? Check out our guide to comma use.