As punctuation marks go, the semicolon is much misunderstood. Many writers use it where a colon or comma would be more appropriate, and vice versa; other writers ignore it rather than risk misusing it. Yet the semicolon is not difficult to master. It has a number of uses, some of which are very handy and some of which you’re unlikely to need.
Style and usage guides often stick to two main categories of semicolon usage; others subdivide these categories and include archaic and less common usages. It may help to bear this in mind, because the categories can overlap slightly. The divisions below are not definitive, but will help break up a rather long post.
1. If any item in a list or series has an internal comma, semicolons can be used to divide the items:
Research was conducted by laboratory technicians in University of Limerick; National University of Ireland, Galway; Trinity College, Dublin; University College Cork; and Dublin City University.
The bag that was found on the hill contained a paperback novel; a lunchbox, empty except for some crumbs; a green fold-up umbrella; and an Ordinance Survey map, which had notes made on it with a pen.
2. Similarly, semicolons can be used to separate coordinate clauses in long sentences. Many of these clauses contain commas, allowing semicolons to emphasize the overall structure and distinct parts of the sentence. They steer the reader through long and sometimes complex passages (though neither of the following examples is particularly complex):
“It would have been in vain for Scrooge to plead that the weather and the hour were not adapted to pedestrian purposes; that bed was warm, and the thermometer a long way below freezing; that he was clad but lightly in his slippers, dressing-gown, and nightcap; and that he had a cold upon him at that time.” (Charles Dickens)
“This is the true joy in life, the being used for a purpose recognized by yourself as a mighty one; the being thoroughly worn out before you are thrown on the scrap heap; the being a force of Nature instead of a feverish little selfish clod of ailments and grievances complaining that the world will not devote itself to making you happy.” (George Bernard Shaw)
3. Semicolons can be used to coordinate independent clauses that are not joined by a coordinating conjunction. Coordinating conjunctions are but, and, so, or, nor, for and yet – basic words that show the relationship between two connected clauses. If any of these is present there is usually no need for a semicolon, unless the writer wants a bigger pause, perhaps to emphasise whatever follows (see quote by Bacon, below).
Sometimes the clauses joined by a semicolon reflect one another, in the sense that they contain mutually antithetical or complementary ideas:
“If youth knew; if age could.” (Henri Estienne)
“In taking revenge, a man is but even with his enemy; but in passing it over, he is superior.” (Sir Francis Bacon)
4. The semicolon has been called a kind of supercomma because it introduces a pause somewhere between that of a comma and a full stop. If you can read clauses as separate sentences, but their respective contents are related closely enough to warrant their sharing a sentence, a semicolon may be the most suitable mark:
“Beauty is worse than wine; it intoxicates both the holder and the beholder.” (Aldous Huxley)
“No man is offended by another man’s admiration of the woman he loves; it is the woman only who can make it a torment.” (Jane Austen)
“The present season was indeed divine; the flowers of spring bloomed in the hedges, while those of summer were already in bud.” (Mary Shelley)
The present post includes two semicolons used in this manner, though with less panache than the examples above.
5. Some style guides recommend using semicolons after each item (except the last) in a bullet point list, if the entries are short enough to begin with lowercase letters. Where bullet points contain full sentences, begin with uppercase letters and end with full stops.
6. Finally, a note on conjunctive adverbs, which include accordingly, after all, anyway, also, besides, consequently, finally, for example, furthermore, hence, however, in contrast, incidentally, indeed, in fact, instead, meanwhile, moreover, namely, nevertheless, nonetheless, now, on the other hand, otherwise, similarly, still, therefore, thus, and undoubtedly.
These can function as conjunctions but they are not true conjunctions – they are transitional words or phrases that join independent clauses. When conjunctive adverbs lie between two independent clauses, they are often best preceded by a semicolon and followed by a comma, though this is not always the case.
Tomorrow will begin brightly; however, rain will spread from the west over the course of the day.
This information could also be phrased as follows:
Tomorrow will begin brightly. However, rain will spread from the west over the course of the day.
Better still, however could be swapped for but, and the punctuation tidied accordingly:
Tomorrow will begin brightly, but rain will spread from the west over the course of the day.
But the following formulations are more common:
Tomorrow will begin brightly, however rain will spread from the west over the course of the day.
Tomorrow will begin brightly, however, rain will spread from the west over the course of the day.
The former treats however as a simple substitute for but, i.e. as a pure conjunction, which it isn’t, while the latter generates a comma splice that renders however ambiguous, since it could belong to either clause. Using however where but (or though, yet or still) would do the job can make a sentence slower and stuffier.