a vs. an

In English writing the indefinite article 'a' is used in congruence with a noun of which not a particular one is indicated as opposed to 'the'. For instance 'the house' is a particular house that can be identified, whereas 'a house' does not reference one house specifically.

When the word following 'a' starts with a vowel sound, it is written as 'an'. Non-vowel sounds are preceded by 'a'. This means that not all consonants are preceded by 'a' and not all vowels are preceded by 'an' as the following examples demonstrate.

Examples
  • a bone
  • an arm
  • an MRI scan (M is pronounced as 'em')
  • a ureter (the 'u' is pronounced as 'you')
  • a history of

Of particular note are words starting with h, as historically some of these words were pronounced with a silent h. As such, they used to be preceded by 'an', but this use has faded. 

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rID: 30716
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