Some writers mistakenly use semicolons to connect fragments or sentences that really should be two separate sentences. Use the semicolon to connect two independent clauses or a series of items.
Joining independent clauses
A semicolon is like a period. While a period keeps two independent clauses apart and turns them into separate sentences, a semicolon joins them to show a close connection. Compare these examples.
I helped the committee all I could. I even searched the back issues of the paper to find evidence.
I helped the committee all I could; I even searched the back issues of the paper to find evidence.
I helped the committee all I could, and I even searched the back issues of the paper to find evidence.
All three examples are punctuated correctly. The semicolon emphasizes a close relationship between the two independent clauses that can stand alone as an independent sentence. Often, you'll find a transitional phrase following a semicolon.
The results of the inquiry were unclear; however, the head of the project resigned.
I planned the new garden to include my favorite flowers; for example, I like daisies, roses, and tulips.
Don't use a semicolon if there is not a close connection between clauses.
It was time to vote; we were sick of the endless wrangling. (correct)
It was time to vote; the secretary carried lunch in and put it on the table. (incorrect, unless the vote relates closely to serving lunch)
You may follow a semicolon that divides independent clauses with a coordinating conjunction. In the following example, it's correct to use a comma before but. Also, because there are already two commas in the second clause, a semicolon better indicates the main break in the sentence.
That night the fox appeared to revive; but when we woke in the morning, full of hope that we had saved it, we were saddened to find its body at the edge of the clearing.
Between items in a series
In a series, use a semicolon between items if the items are particularly long or if they contain commas.
The planning committee included David H. Takahashi, president of the Kiwanis Club; Leroy Carter, head of the small business owners group; Romana Gilbert, editor of the local paper; and Irma Quintero, Spanish department chairperson at the community college.
Jesse's report states that the college, plagued by financial worries, cannot fulfill these needs; that the community response, while positive, has not resulted in financial donations; and that charitable organizations, service clubs, and private donors have been overwhelmed with similar requests.
When semicolons are used in a series, the items in the series do not have to be independent clauses.
Semicolons with quotation marks
When dealing with quotation marks, always place semicolons outside quotation marks.
He asked me to be quiet and mind my “ atrocious manners” ; I told him I'd speak my mind.
Mr. Miser wanted to use words like “ prohibit” and “forbid”; to devise strong, painful punishments for infractions; to publish this book of rules as soon as possible; and, in a bountiful gesture, to distribute it to the orphans with their gruel.