Decades (CMOS 9.33)

Twenty-dollar bills

CMOS 9.33 in the Spotlight

This year isn’t over just yet, but when it does finally come to an end, the current decade will end with it. In other words, we will soon be leaving the 2010s and entering the 2020s.

For writers and editors this means that, for the first time since the 1990s, we will be living in a decade that can be named without resorting to ambiguous or awkward formulations. The decade we are about to enter will be called, quite simply, the twenties.

But how will we refer to the two decades that we are leaving behind?

The Rule and Its Consequences

According to paragraph 9.33 in CMOS 17, “Decades are either expressed in numerals or spelled out (as long as the century is clear) and lowercased.”

For 80 percent of any century, that’s easy: refer to the 1920s* or the twenties, the 1930s or the thirties, and so on, up to and including the 1990s or the nineties. The same holds true for this century: the 2020s or the twenties, the 2030s or the thirties, and so on, all the way to the end. It’s also OK to refer to the ’20s and ’30s and so on as numeric alternatives to the spelled-out versions. Just be consistent, and be sure to get the apostrophe right (’20s, not ‘20s).

You can use a mix of words and numerals that will depend on context. For example, you might refer to “the 1820s” for a first reference to that decade and then, for subsequent references, to the twenties (or the ’20s if you prefer). Or, in the context of recent history, you might be able to refer, without ambiguity, to the nineties (or ’90s) at first mention.

The Trouble Begins at the Beginning

Unfortunately, the forms that work so well for referring to the third through the tenth decades of a century aren’t fully applicable to the first two.

The first decade is the most difficult one to talk about. According to CMOS 9.33, “The first decade of any century cannot be treated in the same way as other decades. ‘The 2000s,’ for example, could easily be taken to refer to the whole of the twenty-first century.”†

“The 2000s,” however, is a tempting shorthand, and many writers have used it.

Wikipedia includes an entry for “2000s (decade),” which it defines as follows: “The 2000s (pronounced ‘two-thousands’) was a decade of the Gregorian calendar that began on January 1, 2000, and ended on December 31, 2009.”

To support such a reading, Wikipedia’s entries for each century spell out the word “century”: “21st century,” “20th century,” “19th century,” and so on.‡ Entries for each decade, then, are in the form “2000s (decade),” “1900s (decade),” and so on.

So, according to Wikipedia, “1700s” means primarily 1700 to 1709, not 1700 to 1799, as a literal reading of the expression would require. (There is no entry in Wikipedia for the 1700s as century.)

That may work for an online encyclopedia, where definitions and explanations are always a click away. But it’s not Chicago style. In Chicago style, “the 1700s” is synonymous with the eighteenth century, and “the 2000s” refers to the entire twenty-first century (see CMOS 9.32).

To refer to the first decade of a century in Chicago style, you need to be either more explicit or more precise. This means either spelling it out or writing it in the form of a numeric range; then, once the century has been established, the first decade can be referred to as such, or you can use a two-digit short form:

the first decade of the twenty-first century or 2000–2009; then the first decade or the ’00s**

but not

the 2000s (except in references to the whole century)

This is not to say that writing “the 2000s” to refer to ’00–’09 (to use another shorthand) is wrong per se; it has been useful especially in journalistic contexts for referring to what is still recent history. Chicago, however, takes the long view. Decades or centuries from now, when the years 2000 to 2009 have become a distant memory, “the 2000s” will be more likely to evoke the century and not the decade.

The Second Decade

The second decade of a century, like the first, resists being named. You could refer to “the teens” or “the tens,” but neither term is sufficiently precise. The first one won’t apply to, for example, the years 2010 to 2012 (the numbers ten through twelve aren’t in the teens); the second suffers from the fact that only the first year of the second decade includes the word “ten” (“two thousand ten” or “twenty ten”).

But there’s no ambiguity about the full numeric form of a second decade. So, to follow Chicago style, write “the 2010s” (or “the ’10s”).


When the year twenty twenty (not to be confused with twenty-twenty or 20/20, which refer to visual acuity) finally arrives, remember that the key to writing about decades is to be precise, on the one hand, and to give your readers sufficient context, on the other. If you can manage both, your decade should get off to a good start.

* In Chicago style, the plural is formed with an s alone (no apostrophe).

† The 2000s could also, of course, refer to the third millennium, but millennia are more typically spelled out.

‡ Further, Wikipedia considers the twenty-first century as beginning on January 1, 2001, and ending on December 31, 2100, and the century known as the 2000s as beginning on January 1, 2000, and ending on December 31, 2099. References in Wikipedia to the latter term redirect to the former.

** The terms “aughts” and (less often) “naughts” are sometimes seen and may be preferred by certain authors, but neither is universally understood in the way that “the twenties” and the like are.

Photo of US$20 bills by Nic McPhee, licensed under CC BY-SA 2.0.

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