A writer should use a dash primarily to indicate an abrupt shift in idea or to add emphasis to a particular part of a sentence. Dashes are often used for creating a dramatic pause or to insert additional information that is not essential to the main point but adds context or detail.
Here's a breakdown of the other options:
-
To set off an introductory word or phrase: This is typically done with a comma rather than a dash.
-
To separate clauses in a compound sentence: A comma, semicolon, or conjunction is generally used for this purpose.
-
To separate items in a list: Commas are commonly used in lists, while dashes can be used in more complex lists, especially those that include internal punctuation, but this is less common.
In summary, dashes are best reserved for situations where a sudden change in thought or an eager emphasis is needed.