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

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A comma can be used before words like 'and', 'or' and 'but' (also covered in lesson Conjunctions).
 


Commas before Conjunctions

Words like 'and', 'or' and 'but' are known as 'conjunctions'. (There are other conjunctions, but these 3 are by far the most common.) As well as conjunctions being used in lists, they can be used to merge two sentences into one. This is very common. When a conjunction is used in this way, it should have a comma before it. (It is called a 'co-ordinate conjunction' in this role.)

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 sentences merged into one with "but" - comma required.)


          comma before "and" in "vitamin, and the skin..." (This is correct.)
                                                (magazine article)

I may consider your plan, or I may disregard it.  
("I may consider your plan" + "I may disregard it." - comma required)

The female applicant must be able to tell jokes and sing, and she must be
able to dance.
("The female applicant must be able to tell jokes and sing." + "She must be
able to dance." - comma required)

The female applicant must be able to tell jokes, sing, and dance.  
(normal conjunction - no comma required)

PLC provided the material, and we built the road.

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 miss him." is a sentence - 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)

I have nothing to offer but blood, toil, tears, and sweat. (Winston Churchill)
(There is no need for the comma before "and" - "sweat" is not a sentence.)

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)
TOO MANY COMMAS? 

When sentences containing commas are merged together using a conjunction, it is possible to use a semicolon instead of a comma. (See lesson Semicolons for more examples.)  However, this is quite an outdated practice in modern writing.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.  
Associated lessons:
 
What are conjunctions?
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
List of easily confused words
 
 

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