By Mark Nichol
Abbreviations are useful, but they can be wickedly tricky little widgets. Keep these points in mind when you truncate words and phrases:
This entry refers not to a or an as abbreviations but to which of the two indefinite articles should precede a given abbreviation. The choice depends not on the first letter of the abbreviation itself but on the sound of the first letter. Therefore, for example, you’d write “an MD after her name,” rather than “a MD after her name,” because the first letter in that abbreviation is pronounced “em” and should therefore be preceded by an.
2. Initials as Adjectives
“I went up to the ATM machine and put in my PIN number to check my IRA account.” And in relating this event, I made three errors. In each case, the last letter of the abbreviation stands for the noun following the abbreviation. This is a job for the Department of Redundancy Department!
3. Metric Abbreviations
Abbreviations for metric measurements either immediately follow the associated numeral (100m for “100-meter dash”) or follow a letter space (“2.2 kg = 1 lb.”); the latter style prevails especially when, as in the example given here, references to both metric-system and English-system measurements occur. But note the absence of periods following the metric abbreviations. Metric abbreviations are always lowercase — with one optional exception: Because of the resemblance of the letter l to the number 1, the abbreviation for liter is often uppercase or italicized, or, when handwritten, styled in cursive writing.
In abbreviations, periods are passe. Period. (Except not: e.g., i.e., etc. But mostly, yes.)
Omit apostrophes with plural forms of abbreviations: “He has two PhDs,” “It lists various NGOs,” “They’re all NIMBYs.” Of course, if the style for the publication in question retains periods (but see the previous point), retain the apostrophe as well: “Several R.N.’s failed the test.”
6. Postal Symbols
Postal symbols are a prescribed set of two-letter abbreviations for states that are sometimes used as shorthand in nonpostal applications. In 1963, to make room for an innovation known as the ZIP code (which phrase has its own entry below), the US Postal Service advocated a two-letter form (CA, for example), but many people persist in incorrectly styling such abbreviations uppercase/lowercase (e.g., Ca.) or appending an extraneous period (CA.).
7. ZIP Code
Those clever folks at the USPS selected this name to imply that mail would arrive at its destination more speedily if the five-digit code was supplied, but ZIP actually stands for something — Zone Improvement Plan — so treat it with all caps.