It’s time to talk about time: specifically, how to write references to units of temporal measurement. This post will note style for increments from seconds to centuries.
Time of Day
Imprecise times of day are generally spelled out: “six-o’clock news,” “half past one,” “a quarter to three,” and “eight thirty,” as well as “noon” and “midnight,” which are preferable to “12 pm” or “12 am,” because technically, these times are neither post meridiem (“after midday”) or ante meridiem (“before midday”). Another solution is to write “12 noon” or “12 midnight,” although the latter term could refer to either the very beginning or the very end of a given day.
The style for precise time is “12:34,” though one-hour increments can be written with or without double zeroes as placeholders: Write “1:00 p.m.” or “1 p.m.,” though the former style is often seen as punctilious.
Much of the world uses a twenty-four-hour clock system, so that the U.S. notation “1:23” is rendered almost everywhere else as “1323,” without a colon. This system is used occasionally in the United States, as in military and technological usage.
Months and Days and/or Years
References to dates consisting of the month and day require no comma (“October 10 is tomorrow”), but set off an appended year with commas (“October 10, 1960, dawned clear and bright”). (Don’t abbreviate the name of the month except in statistical arrays such as graphs and charts or to preserve direct quotations.)
A subsequent mention of a day of the month (in which the month is known but not expressed again), however, should be spelled out in ordinal form (“The 11th, by contrast, was dark and gray”); note that the ordinal should not be styled in superscript form.
Omit a comma before and after the year when the month but not a specific date precedes it: “January 2010 was an unusually wet month.”
A note to writers of American English: Keep in mind that much of the world uses day-month-year notation (“25 December, 2010,” and “25-12-10” as shorthand for that date), so make sure international readers are clear about which number-only notation you use.
Years
Years are almost always rendered in numerals. One major exception honors the convention of not beginning a sentence with a number, but it’s better to recast a sentence than to write, “Two thousand eleven began auspiciously.” Another end run around this problem is to precede the year at the beginning of a sentence with the phrase “The year,” but this strategy introduces nonessential wording and creates an inconsistency if other years are mentioned in the same content.
Years can also be abbreviated (“the spirit of ’76,” “the panic of ’29”), but note that the elision marker is an apostrophe, not an open single quotation mark.
Decades
Decades are displayed in numeral form or spelled out. However, no apostrophe is needed in the former style (“2010s,” not “2010’s”), although some publications retain this archaism. Do, however, precede the elided version of a decade with an apostrophe, just as in informal references to specific years, as mentioned in the previous post.
Phrases that include more than one decade generally use complete numbers for all decades (“the 1920s, 1930s, and 1940s”)” but elision is acceptable in informal usage. Lowercase spelled-out versions (“the nineties”) unless the number is part of the signifier of a cultural era (“the Roaring Twenties”).
Ten-year ranges of decades are divided one of two ways: “2000-2009” (or “2000-09”), or “2001-2010” (or “2001-10”). If your writing project includes multiple references to decades and you mix decade ranges and spelled-out names of decades throughout, make your preference for when a decade starts known, and stick with it.
Note that the first two decades of any given century cannot logically or gracefully be rendered in numerals or words: “1900s” already applies to the entire century, and “1910s” is inelegant because the numbers between 10 and 20 do not have the same naming patterns as the larger numbers; meanwhile, “the oughts” (or “aughts”) and “the teens” are widely considered clumsy solutions.
Centuries and Eras
Spell out or use numerals for names of centuries consistently depending on what style you use for other periods of time, but lowercase the word century.
BCE and CE (“before Common Era” and “Common Era”) are acceptable secular alternatives to AD (anno Domini, or “the year of our Lord”) and BC (“before Christ”), but the traditional forms prevail. Note that syntactically, AD precedes the year, while BC follows it. (You’ll often see these abbreviations rendered in small caps — diminutive versions of uppercase letters — but this practice is fading in frequency.)
Also, although the second number in a range can usually be elided to two digits (“2001-10”), when used with BC or BCE, the full form should be used to avoid confusion because, in these cases, the range falls rather than rises. (In other words, “175-50 BC” is the full expression of a 125-year range, not one of a single generation in which the second number is elided.)