Coordinating Conjunctions

The simple, little conjunctions are called coordinating conjunctions

(It may help you remember these conjunctions by recalling that they all have fewer than four letters. Also, remember the acronym FANBOYS:For-And-Nor-But-Or-Yet-So. Be careful of the words then and now; neither is a coordinating conjunction, so what we say about coordinating conjunctions' roles in a sentence and punctuation does not apply to those two words.)

When a coordinating conjunction connects two independent clauses, it is often (but not always) accompanied by a comma:

• Ulysses wants to play for UConn, but he has had trouble meeting the academic requirements.

When the two independent clauses connected by a coordinating conjunction are nicely balanced or brief, many writers will omit the comma:

• Ulysses has a great jump shot but he isn't quick on his feet.

The comma is always correct when used to separate two independent clauses connected by a coordinating conjunction. See Punctuation Between Two Independent Clauses for further help.

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 

Among the coordinating conjunctions, the most common, of course, are and, but, and or. It might be helpful to explore the uses of these three little words. The examples below by no means exhaust the possible meanings of these conjunctions.

AND

1. To suggest that one idea is chronologically sequential to another: "Tashonda sent in her applications and waited by the phone for a response."
2. To suggest that one idea is the result of another: "Willie heard the weather report and promptly boarded up his house."
3. To suggest that one idea is in contrast to another (frequently replaced by but in this usage): "Juanita is brilliant and Shalimar has a pleasant personality.
4. To suggest an element of surprise (sometimes replaced by yet in this usage): "Hartford is a rich city and suffers from many symptoms of urban blight."
5. To suggest that one clause is dependent upon another, conditionally (usually the first clause is an imperative): "Use your credit cards frequently and you'll soon find yourself deep in debt."
6. To suggest a kind of "comment" on the first clause: "Charlie became addicted to gambling — and that surprised no one who knew him."

BUT

1. To suggest a contrast that is unexpected in light of the first clause: "Joey lost a fortune in the stock market, but he still seems able to live quite comfortably."
2. To suggest in an affirmative sense what the first part of the sentence implied in a negative way (sometimes replaced by on the contrary): "The club never invested foolishly, but used the services of a sage investment counselor."
3. To connect two ideas with the meaning of "with the exception of" (and then the second word takes over as subject): "Everybody butGoldenbreath is trying out for the team."

OR

1. To suggest that only one possibility can be realized, excluding one or the other: "You can study hard for this exam or you can fail."
2. To suggest the inclusive combination of alternatives: "We can broil chicken on the grill tonight, or we can just eat leftovers.
3. To suggest a refinement of the first clause: "Smith College is the premier all-women's college in the country, or so it seems to most Smith College alumnae."
4. To suggest a restatement or "correction" of the first part of the sentence: "There are no rattlesnakes in this canyon, or so our guide tells us."
5. To suggest a negative condition: "The New Hampshire state motto is the rather grim "Live free or die."
6. To suggest a negative alternative without the use of an imperative (see use of and above): "They must approve his political styleor they wouldn't keep electing him mayor."

Authority used for this section on the uses of and, but, and or: A University Grammar of English by Randolph Quirk and Sidney Greenbaum. Longman Group: Essex, England. 1993. Used with permission. Examples our own.

The Others . . .

The conjunction NOR is not extinct, but it is not used nearly as often as the other conjunctions, so it might feel a bit odd when nor does come up in conversation or writing. Its most common use is as the little brother in the correlative pair, neither-nor (see below):

• He is neither sane nor brilliant.
• That is neither what I said nor what I meant.

>It can be used with other negative expressions:

• That is not what I meant to say, nor should you interpret my statement as an admission of guilt.

It is possible to use nor without a preceding negative element, but it is unusual and, to an extent, rather stuffy:

• George's handshake is as good as any written contract, nor has he ever proven untrustworthy.

The word YET functions sometimes as an adverb and has several meanings: in addition ("yet another cause of trouble" or "a simple yet noble woman"), even ("yet more expensive"), still ("he is yet a novice"), eventually ("they may yet win"), and so soon as now ("he's not here yet"). It also functions as a coordinating conjunction meaning something like "nevertheless" or "but." The word yet seems to carry an element of distinctiveness thatbut can seldom register.

• John plays basketball well, yet his favorite sport is badminton.
• The visitors complained loudly about the heat, yet they continued to play golf every day.

In sentences such as the second one, above, the pronoun subject of the second clause ("they," in this case) is often left out. When that happens, the comma preceding the conjunction might also disappear: "The visitors complained loudly yet continued to play golf every day."

Yet is sometimes combined with other conjunctions, but or and. It would not be unusual to see and yet in sentences like the ones above. This usage is acceptable.

The word FOR is most often used as a preposition, of course, but it does serve, on rare occasions, as a coordinating conjunction. Some people regard the conjunction for as rather highfalutin and literary, and it does tend to add a bit of weightiness to the text. Beginning a sentence with the conjunction "for" is probably not a good idea, except when you're singing "For he's a jolly good fellow. "For" has serious sequential implications and in its use the order of thoughts is more important than it is, say, with because or since. Its function is to introduce the reason for the preceding clause:

• John thought he had a good chance to get the job, for his father was on the company's board of trustees.
• Most of the visitors were happy just sitting around in the shade, for it had been a long, dusty journey on the train.

Be careful of the conjunction SO. Sometimes it can connect two independent clauses along with a comma, but sometimes it can't. For instance, in this sentence,

• Soto is not the only Olympic athlete in his family, so are his brother, sister, and his Uncle Chet.

where the word so means "as well" or "in addition," most careful writers would use a semicolon between the two independent clauses. In the following sentence, where so is acting like a minor-league "therefore," the conjunction and the comma are adequate to the task:

• Soto has always been nervous in large gatherings, so it is no surprise that he avoids crowds of his adoring fans.

Sometimes, at the beginning of a sentence, so will act as a kind of summing up device or transition, and when it does, it is often set off from the rest of the sentence with a comma:

• So, the sheriff peremptorily removed the child from the custody of his parents.

Source. http://grammar.ccc.commnet.edu/grammar/conjunctions.htm