Final answer:
A colon is used after an independent clause introducing a list, quotation, or related idea. It also separates titles from subtitles, and can connect two closely related independent clauses to emphasize the second. Unlike a colon, a semicolon should not introduce lists but connects closely related independent clauses.
Step-by-step explanation:
When writing in English, we use a colon after an independent clause (a complete thought that can stand alone as a sentence) when it is followed by a list, quotation, or an idea that is directly related to the independent clause.
Furthermore, a colon is the preferred punctuation mark to introduce lists that elaborate on the preceding clause. For example, “Julie went to the store for some groceries: milk, bread, coffee, and cheese.”
Here, the list of groceries provides more detail about the noun “groceries.” Similarly, a colon can separate book titles from their subtitles.
In addition, a colon can be used to join two independent clauses to emphasize the second clause, signaling that it will complete the idea set up in the first clause.
However, do not confuse this with the usage of a semicolon; a semicolon generally connects two independent clauses that are closely related, or when the second clause restates the first. Unlike colons, semicolons should not be used to introduce lists to an independent clause.