Q:Do you use the indefinite article a or an before an acronym, when it is begins with a different sound from the original term? How about, for example “an NGS project” instead of “a National Geographic Society project”?

A:You decide whether to use a or an depending on whether the first sound of the acronym is a vowel or a consonant. Because the abbreviation NGS begins with the vowel sound eh, (in en) you choose the indefinite article an; but because the word national begins with a consonant sound (n), choose the article a. You probably do this without thinking if you are a native speaker of English, but it can cause problems for people who have learned English as a second language.

Not all abbreviations are acronyms. Dictionaries currently agree that to be an “acronym,” the abbreviation must be pronounced like a word. (See, for example, The American Heritage Dictionary, Second College Edition.) Thus scuba, short for “self-contained underwater breathing apparatus,” is an acronym; but FDR, for “Franklin Delano Roosevelt” is an abbreviation, but not an acronym. Formerly, a few grammarians, notably Wilson Follett, in Modern American Usage (1966), labeled all names made up of initials “acronyms.”

Mr. Follett disapproves of abbreviations in general (he calls them “initialisms”) and he particularly objects to those that are created “backwards” from the word chosen to describe them. He includes such acronyms as AID, which was selected to describe the role of the Agency for International Development,” and CORE to describe the Congress of Racial Equality. He also complains that instead of shortening the title, abbreviating it can make it longer, for people talk of “A.C. and D.C. current,” when the C means “current.” (He might have added “rpms” in which the plural marker–s–is unnecessarily added, and to the wrong word.)

Q:In the March “Language Tips” column you used the phrase used to. I often use that phrase when I talk, but never in writing. In your discussion of “confusing pairs,” you wrote: “Some pairs that used to pose a problem no longer do.” The phrase used to was common in the heavily Polish and German town I grew up in, and my father often told me to avoid it. Is used to now considered proper grammar, or has it always been proper and I was misinformed?

A:You were misinformed. Perhaps your father assumed that the phrase used to was ungrammatical because those who used it spoke ungrammatical English. When I spoke to a group of educated persons in Philadelphia recently, someone in the audience asked whether youse had become acceptable. (The answer: Youse like you-all, as the plural form of you, is not standard English.)

But the phrase used to is acceptable in both speech and writing. It has a long and reputable history, descending from the Latin word usus, the past participle of the verb uti (“to use”). It was borrowed into Old French as user and into Middle English as usen. It has always meant, “to employ, enjoy, or follow as a custom.” When followed by to, it often means “formerly,” and that's the way I used it in my column. Webster's Third provides as illustrations: “Winters used to be harder,” and “It doesn't take as long as it used to.”

The noun use ends with voiceless (s) sound; the verb use ends with a voiced (z) sound. But the influence of the following voiceless t sound ( in to) that follows “used” (pronounced yoost) causes the letter s to become voiceless and the d sound of the past tense to disappear, merging with the voiceless t of the word to. Contrast the voiced sounds (z and d) with the voiceless sounds s and t in, “He used (yoozd) two eggs to make the cake, ”versus, “He used to (yoosto) bake cakes.”

As to its grammatical correctness, the expression used to is in current and wide use, and it is reputable. These three standards for correctness were set forth in the 18^th century by George Campbell, whose two-volume Philosophy of Rhetoric (1776) established criteria for usage which are still authoritative.

In the March “Language Tips,” I mentioned some “confusing pairs.” but there was a typo in my list, which alert reader Ted Nebel, noticed. Instead of the contrast between flagrant and blatant I wrote fragrant and blatant. (The pair flagrant and fragrant could have been listed as another confusing pair!)

I also asked readers to add to the list any confusing pairs they have noticed, and Chicago attorney Jeffrey Liss suggested wistful and wishful. Despite their similar spelling, these adjectives have quite different meanings. Another pair, meritorious and meretricious, derived from the same Latin verb merere (“to earn money”). Both retain the idea of earning money, but they have evolved in opposite directions. Meritorious has ameliorated, and now means “deserving of praise or reward”; meretricious has pejorated, and now means “exhibiting synthetic or spurious attraction,” “resembling a prostitute.”