Commas before conjunctions (e.g., and, or, but)


 
When a word like and, or, and but (called conjunctions) joins two standalone "sentences," you should put a comma before it.

(The real name for a standalone "sentence" within a longer sentence is independent clause.)
 

Put a Comma before a Conjunction If It Joins Two Independent Clauses

Words like and, or, and but are known as conjunctions. (There are other conjunctions, but these three are by far the most common.)

(NB: Conjunctions are often used in lists, and the ruling about using a comma before a conjunction in a list depends on whether you're following US or UK writing conventions, or whether you're an advocate of the Oxford Comma.)

This page is about conjunctions that are used to merge two standalone "sentences" (or independent clauses as they're really called) into one using a conjunction. This is a very common practice. When a conjunction is used in this way, it is usual to place a comma before it.

Examples:

  • He is a great swimmer, but he prefers to play golf.

  • "He is a great swimmer."
    +
    "He prefers to play golf."

    (This is two standalone "sentences" (i.e., independent clauses) merged into one with but. Therefore, a comma is required before but.)

  • I may consider your plan, or I may disregard it.

  • "I may consider your plan"
    +
    "I may disregard it."

    (This is two independent clauses joined by the conjunction or. Therefore, a comma is required before or.)

  • The applicant must be able to tell jokes and sing, and she must be able to dance.
  • (NB: The first and is just a conjunction in a list.)

    "The applicant must be able to tell jokes and sing."
    +
    "She must be able to dance."

    (This is two independent clauses joined by the conjunction and. Therefore, a comma is required before and.)

  • The female applicant must be able to tell jokes, sing and dance. ()
  • The female applicant must be able to tell jokes, sing, and dance. ()
  • (The conjunction and is not joining two independent clauses in this example. Therefore, a comma is not required after sing if you're following UK conventions. In the US (or if you're an advocate for the Oxford Comma), then a comma would be expected after sing.)

    Read more about commas in lists.

  • Drink is the curse of the land. It makes you fight with your neighbor. It makes you shoot at your landlord and it makes you miss him.
  • ("It makes you shoot at your landlord" and "It makes you miss him" are independent clauses. Therefore, a comma required before and)

  • A little dog can start a hare, but it takes a big one to catch it.

  • Basically my wife was immature. I'd be at home in my bath, and she'd come in and sink my boats. (Woody Allen)

  • The play was a great success, but the audience was a disaster. (Oscar Wilde)

  • We make a living by what we get, but we make a life by what we give. (Winston Churchill)

No Comma Necessary for Short Clauses

It is also worth knowing this:

If the two "sentences" (known as independent clauses) are very short, it is acceptable – for style purposes – to omit the comma.

  • Craig joined the Army and Darren joined the Marines.
  • Craig joined the Army, and Darren joined the Marines.
 
TOO MANY COMMAS? USE A SEMICOLON

When indepedent clauses containing commas are merged together using a conjunction, it is possible to use a semicolon instead of a comma before the conjunction.

However, this is quite an outdated practice in modern writing. Use it very sparingly — if at all.

  • Last year, PLC provided the material; and we, L&S Ltd, built the road.
  • (semicolon before and – acceptable for clarity, but quite old fashioned)
Read more about using semicolons before conjunctions.
 

See also:

What are conjunctions?
The Oxford Comma
Commas after a sentence introductions
Commas after a transitional phrase
Commas after interjections (yes, no, indeed)
Commas for parenthesis
Commas in lists
Commas with a long subject
Commas with numbers
Commas with quotation (speech) marks
Commas with the vocative case
Commas with Dear, Hello, and Hi
List of easily confused words