When is a colon properly used in writing?

A colon is properly used in writing after a complete sentence to set off a list. This usage indicates that what follows the colon is directly related to the preceding clause and expands on it. In this case, the complete sentence introduces a subject or topic, and the colon signals that a list of related items or examples will follow.

For example, in the sentence “You will need the following items: a pen, a notebook, and a calculator,” the colon is used to introduce the list of necessary items that support the statement made before it. This function of the colon helps clarify information and presents it in a clear and organized manner, allowing the reader to understand the relationship between the two parts of the sentence.

This rule is consistent with the general usage of colons, which often serve to provide clarification, elaboration, or expansion on an idea that has been presented.