Final answer:
The semicolon is not correctly used in the sentence 'Although they kept playing games; I had to leave and say goodnight.' A comma should be used instead because the first part of the sentence is a dependent clause, not an independent one.
Step-by-step explanation:
In the sentence 'Although they kept playing games; I had to leave and say goodnight,' the semicolon is not used correctly. The correct punctuation mark to use after 'Although they kept playing games' is a comma, not a semicolon. Semicolons should be used to connect two independent clauses that are closely related in meaning and not joined by a coordinating conjunction.
In this case, 'Although they kept playing games' is a dependent clause (also known as a subordinate clause) because it cannot stand alone as a complete sentence. The clause that follows it, 'I had to leave and say goodnight,' is an independent clause because it can stand alone as a complete sentence. The two clauses are connected by the word 'although,' which is a subordinating conjunction, thus a comma is the appropriate punctuation.