Which punctuation mark is used to separate clauses when the second clause explains the first?

The use of a colon to separate clauses is particularly effective when the second clause serves to explain, illustrate, or amplify the first clause. This punctuation mark signals to the reader that what follows will provide further detail or clarification about the statement preceding the colon. For example, in the sentence "She had one goal: to win the championship," the second clause directly elaborates on the singular goal mentioned before the colon.

In contrast, other punctuation marks have different functions. A semicolon typically connects two closely related independent clauses but does not imply an explanatory relationship like a colon does. A comma can separate clauses but is less effective for indicating that the following clause explains the first, as it's often used within compound sentences. A period signals the end of one sentence and the beginning of another, which does not allow for the same explanatory connection found with a colon. Thus, the colon's function of indicating that the second clause explains or elaborates on the first makes it the correct choice in this context.