The main task of the semicolon is to mark a break that is stronger than a comma, but not as final as a full stop. It is used between two main clauses that balance each other and are too closely linked to be made into separate sentences.
- EXAMPLE: The road runs through a beautiful valley; the railway line follows it.
You can also use a semicolon as a stronger division in a complex sentence that already contains commas.
- EXAMPLE: This week's winners are: Joe from Clare, South Australia; Diane from Perth, Western Australia; and Matt from Sydney, New South Wales.
Because each item in the list requires a comma to separate the city from the state, you have to use a semicolon to separate the items themselves.
One reason why you might choose to use a semicolon instead of a full stop is if you wanted to add variety to your sentence structure; for example, you might use a semicolon if you thought you had too many short, choppy sentences in a row.
Another reason to use a semicolon is to draw attention to how related your two clauses are.
- EXAMPLE: I have a big test tomorrow; I can't go out tonight.
The semicolon highlights that the reason you can't go out tonight is that you have a big test tomorrow. You wouldn't write, “English is my favourite food; I can't go out tonight”, because those two main clauses have nothing to do with each other.
Please note: if the emphasis is on the second clause (in other words, if the first clause is followed by a reason or explanation), use a colon!
- EXAMPLE: I can't go out tonight: I have a big test tomorrow.
Avoid using a semicolon and a coordinating conjunction such as 'and', 'so', and 'but' to join two main clauses; that's the job of a comma.
EXAMPLE: I have a big test tomorrow, so I can't go out tonight. (The comma is used.)
Nevertheless, there are a couple of instances where it is acceptable to use a semicolon with a coordinating conjunction.
If you have a long sentence with multiple independent clauses, and some of those clauses contain internal punctuation such as a comma, you can use a semicolon with a coordinating conjunction to make the separation between clauses more clear.
- EXAMPLE: If you want me to go out tonight, you need to help me with my homework first; and if you say no, I'll know that you don't really care about going out.
Since each half of that long sentence has a conditional clause that must contain a comma, it is acceptable to use a semicolon before the “and” that separates those two parts. You could make them two sentences, but you don't have to; and because they are so closely related, it makes a lot of sense to have them be together separated by the semicolon. The “and” after the semicolon is optional in this case.
Conjunctive adverbs are words such as 'however', ‘therefore’, and ‘indeed.’ Such words are used to show cause and effect, sequence, contrast, comparison, or other relationships.
- EXAMPLE: I have a big test tomorrow; therefore, I can't go out tonight. (The comma after the conjunctive adverb is optional.)
- EXAMPLE: I have a big test tomorrow; as a result, I can't go out tonight.
Quick and Dirty Tips. Do Things Better. 'How to use semicolons'. Retrieved from https://www.quickanddirtytips.com/education/grammar/how-to-use-semicolons.
Oxford Living Dictionaries. 'punctuation/semicolon' Retrieved from https://en.oxforddictionaries.com/punctuation/semicolon