Indefinite ArticleThe indefinite article is the word a or an.
More about the Indefinite ArticleThe indefinite article defines something as non-specific.
- I'm a murderer. (This means an unspecified murderer, i.e., not one previously discussed.)
- I'm the murderer. (This means a specific murderer, i.e., the one previously discussed.)
Why Should I Care about Indefinite Articles?There are two commonly discussed issues related to indefinite articles.
(Issue 1) Writing a job title or an office name with a lowercase letterA job title (e.g., president, judge, director) or the name of office (parliament, court, accounts section) is written with a lowercase letter when the word is being used in its dictionary definition (i.e., as a common noun). Some writers are tempted to give such terms capital letters either because the terms seem important (a terrible reason to give a word a capital letter) or because they become confused, knowing such terms can be written with capital letters when they refer to specific people or offices.
If the job title or office name is preceded by the indefinite article (an or a), there is a very high chance it is being used in its dictionary definition (i.e., not as proper noun), in which case you must write it with a lowercase letter.
- The Prime Minister said: "Being a prime minister is a lonely job... you cannot lead from the crowd." (Prime Minister Margaret Thatcher). [correct] (Here, The Prime Minister specifies an individual, but a prime minister does not. It is just the dictionary definition of the term prime minister. In other words, the first one is a proper noun, but the second is a common noun.)
(Issue 2) Choosing an or aAn is used before a vowel sound, and a is used before a consonant sound. (The important word here is sound.) Lots of words and abbreviations that start with vowels (typically u) start with consonant sounds (e.g., unicorn, unique, united, Ouija, one-off), and lots of abbreviations that start with consonants start with vowel sounds (e.g., MOT, LRS, NTU).
- An MoD official and a MAFF official visited an NBC facility of a NATO country. (The M and the N of the initialisms MoD (Ministry of Defence) and NBC (Nuclear Biological and Chemical) are pronounced "en" and "em", i.e., with vowel sounds. The N and M of the acronyms NATO (North Atlantic Treaty Organization) and MAFF (Ministry of Agriculture, Forestry and Fisheries) are pronounced "nuh" and "muh", i.e., with consonant sounds.)
- I had a unique opportunity to strike an unexpected blow. (Unique attracts a because it starts with the consonant sound "yuh". Unexpected attracts an because it starts with a vowel sound "uh".)
There is more on this subject in the entry about articles.
- When a job title (e.g., ambassador) or an office name (e.g., finance office) is preceded by an or a (as opposed to the), it should be written with a lowercase letter.
- Use an before a word that starts with a vowel sound, and use an before a word that starts with a consonant sound.