“A” versus “an”

• Use “a” to precede a word or acronym that starts with a consonant sound:

  • a directory
  • a LAN
  • a unit (the long “u” causes friction)
  • a European
  • a house
  • a one

• Use “an” to precede a word that starts with a vowel sound:*

  • an e-mail message
  • an onion
  • an API
  • an SPD
  • an historical study (the “hi” sound causes no friction)
  • an honorable man
• *The “n” in “an” prevents a speaker from pausing in trying to pronounce two successive vowel sounds.

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