Semicolons
Connecting Independent Clauses
Grammatically, semicolons function like periods. When used to connect independent clauses, a semicolon can always be replaced by a period; this is a good check to make sure you're using it correctly. This page on connecting independent clauses explains this function as well.
Examples
It was hot outside; I enjoyed the beach.
I didn’t study enough; the test was difficult.
The first week of school always seems long; it’s difficult to get back on a schedule.
Adding Clarity to Lists
Semicolons can also separate items in a series when needed for clarity. This often happens when there are commas within items in a series. In this situation, they function as a stronger version of a comma.
Examples
This year, I traveled to Chicago, Illinois; Denver, Colorado; New Orleans, Louisiana; and Boston, Massachusetts.
In the sentence above, it's clear that I traveled to four places, with a city and state given for each. In contrast, using all commas would make it look like I went to 8 places: This summer, I traveled to Chicago, Illinois, Portland, Oregon, New Orleans, Louisiana, and Boston, Massachusetts.
In this class, you will be graded based on the following 5 skills categories: writing; reading and analysis; vocabulary, grammar, and syntax; speaking and listening; and learning process.
The labels of some of these skills categories have commas within them, so I need the semicolons to show the distinctions between the categories.