When should you use a semicolon instead of a comma?

A semicolon should be used instead of a comma in the following situations:

1. To separate two closely related independent clauses without using a coordinating conjunction (e.g., and, but, or). For example: "I have a meeting at 9 a.m.; I need to finish my presentation."

2. To separate items in a list when the items themselves contain commas. This is known as a complex list. For example: "The conference attendees came from various countries, including Canada, Mexico, and Brazil; Europe, including France, Germany, and Italy; and Asia, including Japan, China, and India."

3. To separate independent clauses joined by a conjunctive adverb (e.g., however, therefore, moreover) or a transitional phrase. For example: "She studied hard for the exam; however, she still didn't perform well."

4. To separate independent clauses in a sentence that already contains commas for other purposes, such as separating items in a series. For example: "The book, which is a classic, has been translated into several languages; the movie, based on the book, was a huge success."

It is important to note that semicolons should be used sparingly and appropriately, as overusing them can make writing appear choppy or confusing.