6.2 Semicolons

Image of a semicolon

“Semicolon” by Jelte is in the public domain.

The semicolon could be called a strong comma. Its two main uses are to connect two (or more) sentences that seem very closely related and to set apart a series of items that each have their own internal commas.

You may have had some unhappy encounters with run-ons and comma splices in the past. These two comma faults usually result from the writer’s sense that the sentences involved in the problem are very closely related—the full stop signaled by the period seems like too full of a stop, so the writer erroneously uses a comma. (It’s almost like music; it makes you wonder why we don’t have the equivalent of whole, half, quarter, and eighth rests in punctuation.) Often, these run-on sentences and comma splices can be fixed by substituting a semicolon for the offending comma.

But not always. Some writers go way overboard in sensing close relations between sentences. Well, yes, every sentence in a document is related to every other—they ought to be. But to be joined together with a semicolon, the sentences must be reeeaaally closely related. Here are the general rules for using semicolons in your writing.

Use a semicolon to connect two very closely related sentences.

Examples

“Plaque-fissuring” refers to the formation of an opening from the lumen to the intima; it leads to an intra-intimal thrombus containing not just red cells but mainly fibrin and platelets.

In 1940, philanthropy accounted for 24 percent of the total operating budget of nonprofit hospitals in New York City; by 1948, it had dropped to 17 per cent.

Gray mold is one of the most important fungal diseases in Italian viticulture; its growth causes serious production losses and adversely affects wine quality.

Use a semicolon to separate items in a series that already have commas within them.

Examples

Injury caused by pollutants can easily be mistaken for injury caused by other stresses; or, in the reverse situation, injury symptoms from adverse temperature or moisture relations may resemble, and can be incorrectly attributed to, air pollutants.

Possible research areas announced recently have included genetics, fermentation microbiology, and immobilized biocatalysts; environmental biotechnology, such as metal recovery and waste recycling, is also included.

The heart undergoes two cardiac cycle periods: diastole, when blood enters the ventricles; and systole, when the ventricles contract and blood is pumped out.

An organization may be functional, with responsibility assigned on the basis of buying, selling, promotion, distribution, and other tasks; production-oriented, with production managers for each product category and brand managers for each individual brand in addition to functional categories; or market-oriented, with managers assigned on the basis of geographical markets and customer types in addition to functional categories.

(The sentence above might be better off if broken into bullet points.)

Electric power substations are used for some or all of the following purposes: connection of generators, transmission or distribution lines, and loads to each other; transformation of power from one voltage level to another; interconnection of alternate sources of power; and detection of faults, monitoring and recording of information, power measurement, and remote communication.

A common misuse of the semicolon is plunking one down between what appear to be two complete sentences, but actually aren’t.

Examples

Problem: The slide rule was an important device for scientists and engineers for many years[;] although its use has all but vanished since the advent of the pocket calculator.

Revision: The slide rule was an important device for scientists and engineers for many years, although its use has all but vanished since the advent of the pocket calculator. (The “although” clause is not complete; it can’t stand on its own. The use of the comma in this sentence is correct.)