Punctuation Rules

The Semicolon

A semicolon (;) is like a weak period:

By itself it can separate two main clauses.
It is also used to separate items in a list when the items themselves have internal punctuation.
It also separates two main clauses with the help of a coordinate conjunction when one of the main clauses has internal punctuaion.

Examples

2a. A semicolon separates two main clauses.

Jill fetches water every day; Jack accompanies her only on Saturdays.
The days of summer never seem to to last long enough; even the dog days of summer seem to come and go before a person has a chance to notice them.

2b. A semicolon separates items in a list when the items have internal punctuation.

We sent copies of the memo to Walla Walla, Washington; Traverse City, Michigan; and New Brunswick, New York.
The president spoke to the press on Monday, the day after he decided he wouln't seek a second term; on Wednesday, the day after he changed his mind; and on Friday, when the poles showed a down turn in his popularity rating.

2c. A semicolon and a coordinate conjunction are used to separate two main clauses when one of the main clauses has internal punctuation

They drove to Ottawa that Tuesday morning; and, when they arrived at the courthouse, they nervously sought a parking place.
Fifty-six Thunderbirds are hard to to find these days; but you can buy facsimiles, miniatures with amazing detail, from the Franklin Mint.