The semicolon is a commonly misunderstood punctuation mark. It may be useful to consider the semicolon as something between a comma and a full stop; it both separates and links the clauses it falls between. Though there are varying opinions about the instances where a semicolon is required, the three usages that follow are widely accepted and account for the vast majority, if not all, of such instances.
To link independent clauses
As with the full stop, the semicolon can be used to separate clauses that are grammatically independent; however, unlike the full stop, the semicolon links the two ideas that it separates. Linking similar ideas with a semicolon not only gives your concepts greater continuity, but will also help to vary the tempo of your writing, making it more readable.
Henry speaks slowly when addressing the class; he likes to make sure that all the students can hear him clearly.
To separate clauses connected by conjunctive adverbs
Similarly, the semicolon should also be used before conjunctive adverbs such as ‘however’ or ‘therefore’ when they occur between clauses. Although the comma is sufficient for clauses separated by conjunctions such as ‘and’ or ‘but’, conjunctive adverbs normally require a semicolon to delineate between the two clauses.
Coby’s teaching methods were often considered unorthodox; however, he felt that they were simply more interesting.
Instead of commas in a list
Sometimes the comma is not sufficient to separate the items in a list. This is often the case if the items are unusually long or contain commas themselves. In this instance, the semicolon is used for clarity.
There were three staff members who had returned from the old school: Henry, a physical-education teacher; Michelle, a music teacher and student councillor; and Coby, a maths teacher and swim instructor.
When used carefully, the semicolon adds a level of subtly and nuance to a piece of writing that will not only help you to articulate your meaning, but allow you to show a greater understanding of language itself.