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 being used in a list, a conjunction 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.
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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.)
 Last year, PLC provided the material; and we, L&S Ltd, built the
road.
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Common grammar errors
