Semicolons are used to make sentences more effective, clear, and readable.
Two main USES of semicolons
1. To link two independent – but closely related – clauses:
The policemen checked the area for fingerprints; they hauled out bags of white chalk, brushes, and magnifying glasses.
These two clauses can function as complete sentences on their own. However, when joined by a semicolon, their close relation to one another is made clearer. In addition, it avoids placing two short, choppy sentences close together.
2. To replace commas in a list when the items on the list contain commas themselves:
The students wrote their birthdates on the sheet of paper: May 24, 1993; December 18, 1989; March 15, 1973; and July 25, 1962.
Semicolons are also MISUSED in a number of ways
1. To join two clauses when they are linked with a conjunction:
Brenda kept all of her money stashed under her mattress; but she crammed her utility bills there too.
This is incorrect because the conjunction “but” already effectively joins the two clauses. The correct sentence would read:
Brenda kept all of her money stashed under her mattress, but she crammed her utility bills there too.
2. To link an independent clause to a dependent clause:
When I was growing up, we always had dinner promptly at six o'clock; whether we were hungry or not.
This is incorrect because the clause “whether we were hungry or not,” is not a complete sentence on its own – it must be linked to an independent clause with a comma:
When I was growing up, we always had dinner promptly at six o'clock, whether we were hungry or not.