beforevowel

Beforevowel is a linguistic concept describing how English determines whether to use the indefinite article a or an before a word that begins with a vowel sound. The core rule is simple: use an before a word that starts with a vowel sound and a before a word that starts with a consonant sound. The decision is based on pronunciation, not spelling.

Because pronunciation can diverge from spelling, beforevowel can be nuanced. A word may begin with a vowel letter but a consonant sound, as in university (pronounced /juːnɪˈvɜːrsət i/), which takes a: “a university.” Conversely, a word may begin with a consonant letter but a vowel sound, as in hour or honor, which take an: “an hour,” “an honor.” Acronyms and initialisms follow the same principle depending on how the initial letters are spoken: an FBI agent (the letters begin with a vowel sound when spoken as “eff-bee-eye”) but a NASA scientist (spoken as “en-ess-ay,” starting with a consonant sound).

Numbers and certain loanwords can also trigger the rule based on pronunciation. For example, an eight-hour shift uses an because eight starts with a vowel sound, while a two-day period uses a because two starts with a consonant sound. In practice, speakers rely on listening to the initial sound rather than the initial letter, which explains why exceptions exist across words and contexts.

Usage notes include that the trend can vary by dialect and formality, and that newer or borrowed terms may prompt quick adjustments as pronouncing habits evolve.