A vs. an
Also known as: indefinite articles
Use "a" before words that begin with a consonant sound and "an" before words that begin with a vowel sound. The choice depends on pronunciation, not spelling — "an hour" but "a university."
"A" and "an" are the two forms of the English indefinite article, used before singular nouns that aren't specifically identified. The rule for choosing between them is entirely about sound: use "a" before a word that starts with a consonant sound, and "an" before a word that starts with a vowel sound.
The tricky cases are words whose spelling and pronunciation disagree. "Hour" and "honest" begin with the letter h but a vowel sound, so they take "an": an hour, an honest answer. "University" and "one" begin with vowels on paper but consonant sounds ("yoo" and "wuh"), so they take "a": a university, a one-time fee. Abbreviations follow the same logic — an MBA (because "em" starts with a vowel sound) but a NASA program.
The article also attaches to the sound of whatever word immediately follows it, not the noun itself. You'd write an apple but a red apple, and a report but an updated report. Reading the phrase aloud is the most reliable test: if the next word starts with a spoken vowel, use "an."
Standardized tests like the ACT include a vs. an among their conventions-of-usage questions, favoring exactly these sound-versus-spelling traps — h-words, u-words, "one," and initialisms — so train your ear rather than memorizing letters.
Key takeaways
- Choose "a" or "an" based on the first sound of the next word, not its first letter.
- Silent-h words take "an" (an hour, an honest mistake); "yoo"- and "wuh"-sounding words take "a" (a university, a one-way street).
- The article matches the word directly after it: an apple, but a red apple.
- Abbreviations follow pronunciation: an MBA, an FBI agent, a UFO.
- The ACT tests this rule with sound-versus-spelling traps, so read the phrase aloud.