In normal prose, a semicolon is used between two independent clauses to indicate a closer connection between them– whether logical, causal, sequential, or associative – than would be implied by a period. The difference can be illustrated by the following two passages:
1. You need to prepare for your trip. It often rains in London.
2. You need to prepare for your trip; it often rains in London.
In the first of these examples, the relation between the two clauses would need to be substantiated by the context in which they occur and other information provided therein. In the second, the implication is that preparation is necessary because it often rains.
When certain adverbs are used to join independent clauses, they should be preceded by a semicolon. These are usually adverbs which indicate a certain logical relation between the two clauses, such as however, therefore, thus, hence, besides, accordingly, and so on. A common error is to use a comma in such situations, as in the following:
1. I like sushi, however, I can’t stand raw Carpaccio.
The correct arrangement would be:
2. I like sushi; however, I can’t stand Carpaccio.
A semicolon can also be used instead of a coordinating conjunction to link two clauses:
3. She knows the play well; she’d acted in it seven times.
Semicolons may also be used after phrases such as for example, namely, and so on when these introduce an independent clause, although commas are more frequently used in this situation in contemporary prose.
1. For example; he falls asleep in every movie he goes to.
2. For example, he falls asleep in every movie he goes to.
are equally correct.
While an independent clause which begins with a conjunction is normally set off from the rest of the sentence by a comma, a semicolon can also be used, either to emphasize the separation of the clauses, and thus intensify the dramatic or emotional force of the statement, or, if the second clause contains its own internal punctuation, to enhance clarity of meaning. The following are examples of these two respectively:
1. She claimed she loved none but him; yet she always left the room to answer her phone.
2. Barry wanted to go home; but Alisa, knowing he would get lost in his X-box, gorge himself on popcorn, and fall asleep on the floor, protested.
Another use, related to the second listed above, is to separate items in a series which themselves contain punctuation. This, again, is for the sake of clarity, and would look something like the following:
1. We have been to three foreign countries: Ireland, which was green and wet; Brazil – Dave’s favorite – which was hot, loud and crazy; and Thailand, where we mastered the art of scooter riding.
In other circumstances, the items of a series can be separated by commas:
2. Life is nasty, brutish, and short.
To be sure, however, you may want to check out the entry for semicolon in the Oxford English dictionary online. Even better would be to enlist the assistance of a professional editor. Being trained and experienced in the technical aspects of writing, a professional editor will be able to make sure that your meaning, grammar and presentation is clear and flawless. Think about how much time and effort you’ve put into your writing, and what you hope to achieve by it. Wouldn’t it be silly to let that all go to waste because of a few minor errors?