Commas and Conjunctions

by Craig Shrives

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Should I use a comma before a conjunction?

Writers often ask whether they should put a comma before a conjunction (e.g., "and," "or," "but"). Use a comma before a conjunction that merges two sentences into one. Also, use a comma before the conjunction in a list of three or more items, but only if that's your local convention.

(1) Use a comma before a conjunction if you're merging two "sentences" into one with a conjunction.

For example:
I like pies
+
, but
+
I hate sausage rolls.
  • Sentence 1: I like pies.
  • Sentence 2: I hate sausage rolls.
  • The Two Sentences Merged: I like pies, but I hate sausage rolls.
  • (The sentences have now become independent clauses (i.e., clauses that can stand alone as sentences) in a compound sentence. When your conjunction (here, "but") joins two independent clauses, put a comma before it.)
(2) Use a comma before a conjunction in a list of three or more items if that's your local convention.

With lists, if there are just two list items, don't use a comma before the conjunction. For example:
  • I like burger and fries.
With three or more list items, use a comma if you're an American. For example:
  • I like burger, shake, and fries. ()
  • (The comma before "and" is called a "serial comma" or an Oxford Comma.)
Most Brits do not use a serial comma. For example:
  • I like fish, chips and peas ()
  • (Be aware that lots of institutions in the UK use the Oxford Comma, i.e., they use the same convention as Americans.)
Note: If breaking your normal convention with the Oxford Comma makes your text less ambiguous, then break your normal convention.

Infographic Explaining Commas before Conjunctions

This flow diagram explains when to use a comma before a conjunction:
commas and conjunctions

More about Commas before Conjunctions

Unfortunately, there is no simple rule like:
  • Always use a comma before "and."
  • (This is not a rule!)
  • Never use a comma before "and."
  • (This is not a rule either!)
The rules for using a comma before a conjunction (such as "and," "or," and "but") depend on how the conjunction is used.

Use a Comma to Join Two Independent Clauses

When two standalone sentences (or independent clauses) are joined together using a conjunction (e.g., "and," "but," "or"), the conjunction should be preceded by a comma.
We eventually found the cave
+
, but
+
Jack was not there.
  • Sentence 1: We eventually found the cave.
  • Sentence 2: Jack was not there.
  • The Two Sentences Merged: We eventually found the cave, but Jack was not there.
  • (The "sentences" have now become independent clauses in a compound sentence. When a conjunction (here, "but") joins two independent clauses, it is preceded by a comma.)

Examples of a Comma before a Conjunction That Joins Two Independent Clauses

In these examples, the conjunctions are in bold:
  • Our team was given 2 minutes' notice, but theirs had been training for weeks.
  • (When two complete "sentences" are merged into one using a conjunction, the conjunction should be preceded by a comma.)
  • I have spoken to Sarah, and she has confirmed the delivery date.
  • ("I have spoken to Sarah." + "She has confirmed the delivery date". The conjunction "and" is correctly preceded by a comma.)
  • I have spoken to Sarah, and confirmed the delivery date.
  • (The conjunction "and" should not be preceded by a comma because "confirmed the delivery date" is not a complete sentence, i.e., it is not an independent clause. This is just a list with two list items: "spoken to Sarah" and "confirmed the delivery date.")
  • We built the hut in an hour and then painted it.
  • (This is correct with no comma because "then painted it" is not an independent clause.)

More about Commas and Sentence Structure

A sentence made up of two halves, either of which could be a standalone "sentence," is known as a compound sentence. The conjunction that joins the two halves of a compound sentence is preceded by a comma.

Here are some other sentence types:
  • I love milk.
  • (This is a simple sentence.)
  • I cannot drink it when it is warm.
  • (This is a complex sentence. A complex sentence is made up of an independent clause ("I cannot drink it") and a dependent clause ("when it is warm").)
  • I love milk, but I cannot drink it when it is warm.
  • (This is a compound sentence. The comma before "but" is correct.)
Read more about using commas with the different sentence structures.

Comma with Conjunctions in Lists

Don't Use a Comma to Join Two List Items

When there are two items in a list, there is no need to separate the list items with a comma. For example:
  • Fish and chips
  • She would only eat ham and eggs.
  • I have never been to London, or Paris.
  • (With two list items, there is no need for the comma.)

With Three List Items, Use a Comma If You're an American (or an Advocate for the Oxford Comma)

When there are three or more list items, things start to get complicated. There are two conventions. Generally speaking, Americans will use a comma, but Brits won't. (There's more on this below.) For example:
  • Fish, chips, and peas ()
  • Fish, chips and peas ()
  • I have never been to London, New York, or Paris. () ()
The comma before a conjunction in a list is called a serial comma or an Oxford Comma. Be aware that lots of British institutions use the Oxford Comma, and lots of Americans omit it. So, the "national conventions" explained above are not strictly followed in either country. There are also times when you should break whatever convention you're following to make your text clearer.

The Oxford Comma causes great debate among grammarians. The bottom line is this: Use the convention that your institution uses and then be consistent throughout your document. Read more about commas in lists. Read more about the Oxford Comma.

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See Also

What are conjunctions? List of 50 conjunctions What is an Oxford Comma? Commas in lists Conjunctions and semicolons Can you start a sentence with "and" or "but"?

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