Here's why:
* Stronger than a comma: Semicolons indicate a more substantial pause than commas, separating two closely related independent clauses that could stand alone as sentences. They suggest a stronger connection between the ideas than a comma would.
* Not as strong as a colon or period: Semicolons don't completely sever the connection between the clauses like a period does, and they don't introduce a list or explanation like a colon.
Example:
* Comma: "The sun was setting, the birds were singing."
* Semicolon: "The sun was setting; the birds were singing." (More emphasis on the connection between the two clauses)
* Colon: "The sun was setting: the birds were singing." (Introduces an explanation or list)
* Period: "The sun was setting. The birds were singing." (Complete separation of the two clauses)