1. Use a comma before the conjunction (and, for, but, or, nor, so) that joins the two independent clauses in a compound sentence.
Examples: I like working outside, and I also enjoy reading.
He got out of school early, so he took a nap.
2. Use a comma after relatively lengthy introductory phrases or dependent (subordinate) clauses. It is important to note that a comma should not be used when the clause or phrase comes at the end of the sentence as illustrated by the third example.
Examples: In order to be successful, one must learn to write well.
After she learned the rules for using commas, her grades improved.
Her grades improved after she learned to use commas correctly.
3. Use commas to separate items in a series. Be sure to insert a comma before the conjunction that precedes the last item unless your teacher or style manual specifically tells you to exclude them.
Example: Amy ordered two hamburgers, a Coke, and a large order of fries.
4. Use commas before and after non-essential elements (parts of the sentence providing information that is not essential in order to understand its meaning).
Example: Horace Mann Elementary, which is the smallest school in the district, enrolls only 160 students.
5. Use commas between coordinate adjectives (of equal importance) that modify the same noun. Do not separate adjectives of unequal importance. A good way to determine if the adjectives are of equal importance is to reverse them in the sentence. If the sentence does not read well after the reversal, do not use a comma between them. The second example below clearly illustrates this point. Reversing the adjectives (blue big eyes or red bright hair) simply doesn't work!
Examples: By the end of the game, the field was a slippery, wet mess.
Her big blue eyes and bright red hair made her strikingly beautiful.
6. Use commas to separate the elements of dates and places.
Examples: The date was June 12, 1999.
He was born in St. Cloud, Minnesota.
7. Use a comma before a direct quotation. Also, as shown in the example, commas (and periods as well) go inside the quotation marks.
Example: When asked if he had studied for the test, Paul replied, "Only a little," and his grade showed it!
8. Use commas before and after words and phrases like however and never the less that serve as interrupters.
Example: Adam did not like math. He was, however, very successful in his math classes.
1. Use a semi-colon in place of the comma and conjunction to separate the two independent clauses in a compound sentence.
Example: I like working outside; I also enjoy reading.
2. Use a semi-colon before the conjunctive adverb (such as however and therefore) that joins two independent clauses. Be sure to put a comma after the conjunctive adverb.
Example: I like working outside; however, I also enjoy reading.
3. Use semi-colons to separate elements in a series if they contain internal punctuation.
Example: On his fishing trip, Jeff caught rainbow, brook, and lake trout; large-mouth, small mouth, and white bass; and a few northern pike.