One subscriber wrote to ask how to determine whether to use a or an in front of a noun. Like many of us, he had been taught simply to put a in front of consonants and an in front of vowels, but he realized that this oversimplified rule didn’t work in every case.

Rather than looking at the actual letter with which a noun, noun phrase, acronym, or initialism begins, however, we should consider the sound we hear at the beginning.

The article used in each of the following phrases is correct:

  1. an umbrella
  2. a unicorn
  3. a fly
  4. an FBI agent
  5. a Federal Bureau of Investigation agent

In phrase 1, we use an because the word umbrella starts with a vowel sound.

The word unicorn in phrase 2, on the other hand, begins with the long u sound, which we pronounce yew.

Thus, we hear a consonant sound even though we see a vowel.

The same criteria apply to the phrases “a fly” and “an FBI agent.”

In the former we hear the consonant sound f, while in the latter the abbreviation starts with the short e vowel sound. What we hear is eff.

When we spell out the words denoted by the abbreviation “FBI,” as in number 5, we hear the consonant sound made by the letter f and must use the article a.

A or An Is Especially Tricky with the letter 

As Webster’s points out, often when a word starts with the letter h and begins with an unstressed (or weakly stressed) syllable, writers tend to use an, especially when speaking.

Many people would say, for example, “an historian” rather than “a historian” because we place the stress on the second syllable, not the first one.

The Chicago Manual of Style, however, ignores the issue of stressed syllables and advocates the use of a since the word historian (as well as similar words, like historical) starts with the consonant sound h.

If that sounds odd to you, consider that we would never say “an hysterectomy” or “an horse.”

If a word starts with a silent letter, as in the words herb and heir, we hear the vowel sound and so should use an.

Be sure to check out other confusing word pairs on this site, such as bad and badly, who and whom, lay and lie, and effect and affect.

If you can think of other confusing word pairs you would like to see addressed here, let us know.


  1. ___ medical doctor
  2. ___ M.D.
  3. ___ State Department of Education initiative
  4. ___ SDE initiative
  5. ___ honor
  6. ___ heir
  7. ___ history professor
  8. ___ historical monument


  1. a medical doctor
  2. an M.D. (we hear em)
  3. a State Department of Education initiative
  4. an SDE initiative
  5. an honor (silent h)
  6. an heir (silent h)
  7. a history professor
  8. a historical monument (per Chicago but not per Webster’s)

Copyright 2001 Get It Write. Revised 2019