Final answer:
A semicolon is used to link two independent clauses when they are closely related in ideas, often when the second clause restates or further explains the first. It should not be used with dependent clauses or merely phrases.
Step-by-step explanation:
We use a semicolon to connect two independent clauses when the ideas in both clauses are closely related. For instance, a semicolon is appropriate when the second clause restates the first, or when it adds a related observation or argument without the use of a coordinating conjunction (e.g., for, and, nor, but, or, yet, so). For example, "The project is overdue; we underestimated the time required to complete it."
Using a semicolon can also clarify a sentence where items in a list already include commas. Remember, avoid using semicolons with phrases or to connect an independent clause with a dependent clause. Instead, use periods, coordinating conjunctions, or commas (in the case of dependent clauses) as appropriate.