A comma is also correct when and is used to attach the last item of a serial list, although many writers (especially in newspapers) will omit that final comma:
• Ulysses spent his summer studying basic math, writing, and reading comprehension.
When a coordinating conjunction is used to connect all the elements in a series, a comma is not used:
• Presbyterians and Methodists and Baptists are the prevalent Protestant congregations in Oklahoma.
A comma is also used with but when expressing a contrast:
• This is a useful rule, but difficult to remember.
In most of their other roles as joiners (other than joining independent clauses, that is), coordinating conjunctions can join two sentence elements without the help of a comma.
• Hemingway and Fitzgerald are among the American expatriates of the between-the-wars era.
• Hemingway was renowned for his clear style and his insights into American notions of male identity.
• It is hard to say whether Hemingway or Fitzgerald is the more interesting cultural icon of his day.
• Although Hemingway is sometimes disparaged for his unpleasant portrayal of women and for his glorification of machismo, we nonetheless find some sympathetic, even heroic, female figures in his novels and short stories.
Beginning a Sentence with And or But
A frequently asked question about conjunctions is whether and or but can be used at the beginning of a sentence. This is what R.W. Burchfield has to say about this use of and:
There is a persistent belief that it is improper to begin a sentence with And, but this prohibition has been cheerfully ignored by standard authors from Anglo-Saxon times onwards. An initial And is a useful aid to writers as the narrative continues.
from The New Fowler's Modern English Usage
edited by R.W. Burchfield. Clarendon Press: Oxford, England. 1996.
Used with the permission of Oxford University Press.
The same is true with the conjunction but. A sentence beginning with and or but will tend to draw attention to itself and its transitional function. Writers should examine such sentences with two questions in mind: (1) would the sentence and paragraph function just as well without the initial conjunction? (2) should the sentence in question be connected to the previous sentence? If the initial conjunction still seems appropriate, use it.