Indefinite Articles Before Acronyms: Is It “A URL” or “AN URL”?

Is it “a LED display” or “an LED display”? And would you say “a URL” or “an URL”?

Choosing between a or an is one of those grammatical things that native English speakers might have an instinct for, but it’s possible they’ve never actually heard the official rule. And if English isn’t your first language, never fear! This particular rule is much simpler and more logical than most English grammar rules.

A and An: The Indefinite Articles

There are three articles in the English language: a, an, and the. An article is “a limiting adjective that precedes a noun or noun phrase and determines its use to indicate something definite (the) or indefinite (a or an)” (The Chicago Manual of Style). So yes—”a” and “the” are technically adjectives!

In plain English, this means that an article tells us whether something is “definite,” meaning a specific, singular object (i.e., the bag, not just any old bag) or “indefinite,” meaning a nonspecific object (i.e., a student, not any particular student).

So if you’re talking about a specific book, you’d use the definite article the: “The book I meant to bring was accidentally left on the kitchen table.” We’re not talking about any old book—there was one specific book that I meant to bring.

But if you’re just talking about a nonspecific, general book, you’d use an indefinite article instead: “I meant to bring along a book, but I forgot.” By saying A book instead of THE book, you’re taking away the specificity. There wasn’t one single book that you meant to bring—you just had intended to bring along some kind of book.

Here’s another example:

The first example uses the indefinite article a; from that little word, we can infer that there isn’t one specific couch that we know you’ve got your eye on—we’re just asking if you’re going to buy ANY couch.

The second example uses the definite article the. This implies that we know about one specific couch that you’ve been thinking about purchasing, and we’re wondering if you’re finally going to buy it.

So now that we know the difference between definite (the) and indefinite (a, an) articles, it’s time to narrow things down even further: When it comes to indefinite articles, when should you use a, and when do you use an?

A or An: Which One Should You Use?

The choice between a or an comes down to the word that comes directly after it.

If the beginning of the word that comes after the indefinite article SOUNDS like a VOWEL, you need an. If the beginning of the word that comes after the indefinite article SOUNDS like a CONSONANT, you need a.

Notice that we’re talking about SOUNDS here, not letters.

Some consonants start with a vowel sound, like “L” (pronounced “el”) and “M” (pronounced “em”).

Some vowels begin with a consonant sound, like “U” (pronounced “you”) and the “O” in “one” (pronounced “won”).

So you should ignore the actual first letter and instead focus on what that letter actually sounds like when you say it out loud.

A Comes Before Words Beginning With a Consonant Sound

The indefinite article a comes before words that begin with a consonant sound.

• a business
• a cat
• a eulogy (pronounced “you-lo-gy”)
• a onetime visit (pronounced “won-time”)

Rather than focusing on the letters themselves, think about spelling out the word phonetically.

After winning the race, I had a euphoric feeling.

Although euphoric begins with not one but TWO vowels, it sounds like it starts with a consonant (the sound “you”), so it needs a before it, not an.

An Comes Before Words Beginning With a Vowel Sound

The indefinite article an comes before words that begin with a vowel sound.

• an ice-cold soda
• an apple
• an effigy

Again, we’re talking about sounds, so even if the next letter is a consonant but just sounds like it begins with a vowel, choose an:

I watched an X-files episode last night.

X is a consonant, but it’s pronounced “ex,” which means it sounds like it starts with a vowel; that means we need an!

But What About “H”?

Generally, our rule about vowel or consonant sounds is still true where “h” words are concerned. If the “h” is NOT pronounced and the word begins with a vowel sound, use an:

We have about an hour before the plane departs.

If the “h” IS pronounced, you need a, because “h” is a consonant:

I had a hard decision to make.

You might see some old-school grammarians using an before “h” words like historian, hysterical, and habitual because the “h” sound used to be silent in those words (which meant the words began with vowel sounds). However, Americans usually pronounce the “h” at the start of those words now, so it’s technically correct to use a instead.

How To Use A and An Correctly Before Acronyms

Finally we get to the acronym part! When you must choose between a and an before an acronym or abbreviation, just keep applying that vowel vs. consonant sound rule. (I know—English grammar is NEVER this easy. It’s a rare situation where one simple rule keeps holding true!)

If the first letter or syllable SOUNDS like a consonant, use a:

• a PDF file
• a ZIP code
• a BTS look
• a URL (pronounced “you-are-el”)
• a CBS newscaster
• a 007 agent (pronounced “double-oh-seven”)
• a NATO agreement

If the first letter or syllable SOUNDS like a vowel, use an:

• an ATM
• an IRA account
• an MBA degree (pronounced “em-bee-a”)
• an LED display (pronounced “el-ee-dee”)
• an ROTC program (“ar-oh-tee-cee”)
• an FAQ list (“ef-a-cue”)
• an NBA game (“en-bee-a”)

You might’ve noticed that the last example for both a and an is an acronym that begins with “N.” How can that be?

The first one—”a NATO agreement”—involves a true acronym; that is, we read “NATO” as a single word (not saying each of the letters individually). As a result, this word starts with a consonant sound, “N.” That means we need a before it.

The second example—”an NBA game”—is actually an initialism, which means we read each letter individually. Thus, this abbreviation actually starts with a vowel sound, “en,” and we need an before it.

Read the words out loud and stick to the SOUNDS, and you’ll be able to choose between a and an in any situation!

Sources:

• The Chicago Manual of Style. 17th ed. Chicago, IL: The University of Chicago Press, 2017.
• Ebbitt, D. R., and W. R. Ebbitt. Index to English. 8th ed. New York: Oxford University Press, 1990.
• Einsohn, Amy. The Copyeditor’s Handbook. 3rd ed. Berkeley and Los Angeles, California: Univ of California Pr, 2011.
• Merriam-Webster. Merriam-Webster’s Dictionary of English Usage. 14th ed. Taunton, MA: QuadGraphics, 2016.