How we change what others think, feel, believe and do
Use semicolons to separate two sentences that are closely related. The two sentences must each be able to stand alone without modification.
Use semicolons in this way to avoid seeming abrupt and impolite.
Do not use the semicolon as a separator when the colon should be used (contrastive separation or causal connection).
Semicolons can also separate items in a list when the items are multi-word, and especially if they contain commas or the use of commas as list separators could cause confusion.
The car has a large engine; this power is used to accelerate quickly.
We are unable to meet as planned; please accept our apologies.
The people who are coming are: the mayor, Michael Green; his wife, Jane Green; Rachel Smith; the gamekeeper and the gardener, Sam Gee.
Using a semicolon to appear polite is effective in using the Hurt and Rescue principle. By connecting more closely a hurtful statement with an apology or other rescue, less time is left for the other person to react negatively to the hurt. The longer pause than a comma is important socially as a mark of respect. The balance of respectful pause and rapid rescue is a delicate activity that can bring subtly to your communications.
Historically, colons and semicolons were often used interchangeably. Poets in particular used them as devices of division. More recently, it is used rather infrequently, often because authors are uncertain of its proper use.