Between Two Independent Clauses
A semicolon is often used between two closely related independent clauses.To use the semicolon properly, therefore, one has to understand the difference between independent and dependent clauses.

The short description is an independent clause can stand by itself as a separate sentence; a dependent clause cannot.

Here are some examples of two independent clauses connected by a coordinating conjunction (FANBOYS—for, and, nor, but, or, yet, and so are the most common coordinating conjunctions). Next you'll see the two independent clauses broken into two separate sentences.Then we'll show you the same clauses connected with a semicolon. In this use, the semicolon replaces  the coordinating conjunction.

1. Joan needed a new coat, and she drove to the mall to buy one.
   The two sentences: Joan needed a new coat. She drove to the mall to buy one.
   With the semicolon: Joan needed a new coat; she drove to the mall to buy one.
   
2. The bicycle’s wheel was broken, but Billy didn’t have the money to get it fixed.
   The two sentences: The bicycle’s wheel was broken. Billy didn’t have the money to get it fixed.
   With the semicolon: The bicycle’s wheel was broken; Billy didn’t have the money to get it fixed.
   
3. Sam took the roast from the oven and I carried it to the dining room table.
   The two sentences: Sam took the roast from the oven. I carried it to the dining room table.
   With the semicolon: Sam took the roast from the oven; I carried it to the dining room table.

Notice in the examples above that each sentence that contains a semicolon also is composed of two closely related statements. Semicolons are NOT used between two unrelated statements.

The following sentences are examples of two unrelated statements connected with a coordinating conjunction:

1. Alex flew to Arizona this morning, and we went to a ball game.
   The two sentences: Alex flew to Arizona this morning. We went to a ball game.
   WRONG use of semicolon: Alex flew to Arizona this morning; we went to a ball game. The clauses are independent, but the ideas are unrelated. This use of a semicolon is incorrect.

2. The clerk asked my name, and I reached into my pocket for a mint.
   The two sentences: The clerk asked my name. I reached into my pocket for a mint.
   WRONG use of semicolon: The clerk asked my name; I reached into my pocket for a mint. Again, the clauses are independent, but the ideas are unrelated. This use of a semicolon is incorrect.

Semicolons can be very useful between independent clauses when you want an idea to flow without stopping for a period, but you want a little more hesitation than a comma provides. Just take a moment to make sure you’re using it correctly, and remember, independent clauses are able to stand alone as a sentence.

To Separate a Series
Use a semicolon to separate items in a list or series if any of the items contain commas.

1. The bag contained softballs; bats; the catcher’s mask, chest protector, and shin guards; and a couple of extra gloves.
   The catcher’s gear (mask, chest protector, and shin guards) contains commas and needs to be kept separate in the list. Using semicolons before and after it makes this clear, and semicolons need to be put after each of the other items for consistency.
   
2. Her hall closet contained walking, running, tennis, and golf shoes; flannel, suede, and denim jackets; assorted hats; and a scarf.
   The items that contain commas—shoes and jackets—are correctly separated by semicolons. A semicolon also follows hats for consistency in the series.

To Separate Lengthy Clauses
Use a semicolon (rather than a comma) between independent clauses joined by a coordinating conjunction if the clauses already contain commas or if the clauses are lengthy . Note that in this type of sentence, the coordinating conjunction that comes after the semicolon can be kept.

1. Joan needed a new coat, a new dress, and new shoes; and she drove to the mall to buy them.
   
2. The bicycle’s wheel was broken, the seat was jammed, and the handlebars were bent; but Billy didn’t have the money to get them fixed.
   
3. Sam opened the oven, took out the roast, potatoes, carrots, and onions, and then sliced the roast and put some of the vegetables around it and some in separate dishes; and I made several trips to carry everything to the dining room table.

With a Conjunctive Adverb or a Transitional Phrase
Another common use of a semicolon is with a conjunctive adverb (adverbs that join independent clauses): however, moreover, therefore, consequently, otherwise, nevertheless, thus, etc.

Conjunctive adverb examples:

1. Joan needed a new coat; therefore, she drove to the mall to buy one.
   
2. The bicycle’s wheel was broken; however, Billy didn’t have the money to get it fixed.
   
3. Sam took the roast from the oven; consequently, I carried it to the dining room table.

And use a semicolon with a transitional phrase that links two independent clauses: because of which, as a result of, not to mention, etc.

Transitional phrase examples:

1. The board met this past Thursday; as a result, they passed some new rules.
   
2. We chose a new place to dine; in retrospect, that was a mistake.
   
3. Babe Ruth hit a lot of home runs; because of which, people cheered for him.

To Sum Up
Use semicolons:

1. To replace conjunctions in linking independent clauses.
2. Only with independent clauses that are closely related.
3. To separate a series when any item contains commas.
4. To separate lengthy clauses or ones that contain commas.
5. With conjunctive adverbs—however, moreover, therefore, etc.
6. With transitional phrases—because of which, as a result of, not to mention, etc.