The general rule is that, “an” is to be used before a vowel and “a” is to be
Used before a consonant.
This rule is applicable in most of the situations.
But in some cases the word “an” is used before consonant and at the same time the word “a” is used before a vowel.
Because, the actual usage of "a" and "an" in English is not related to whether,
it has to come before a vowel or a consonant.
It is totally depends on the sound of the first letter, i.e., whether it is taking the sound of a vowel or a consonant.
lets see in detail;
1. Words begin with a vowel but not using "an" before it.
Case 1: Few of English vowels take two sounds. For example the English letter ‘u’ sometimes take the sound "ah" and sometimes "yoo".
Case 2: In case of the word one, the first letter is taking the sound of "wa" which is not a vowel sound. So "one" will not have the prefix "an" instead it will have "a". For example: "a one-day match".
Case 3: There are several English words for which the first letter will be silent. When that silent letter is a vowel then the word will take the sound of the second letter. And, if the second letter takes the sound of a consonant then it will have the prefix as "a" before it.
- For example: in the word Euro the first letter
"E" is silent, and it takes the second letter as the initial sound "yoo", which is not a vowel sound. So it is "a Euro" not
eucalyptus, euglena, eukaryote ,eulachon,
eulogy, eureka, euro, Euro-American, European bison, ewe, one, Ukrainian,
unary, uni, unicorn, uniform, union, unique, unit, unite, unity, univalent,
universal, universalism, Universalism, universe, university, univocal, Unix,
uranium, urinal, urinalysis, urine, uro, usability, usable, usage, use, user,
US-ian, using, usufruct, usufruction, usufructuary, utensil, uterus, utile,
utilitarian, utility, uvula, uvular, etc.
2. Words begin with consonant but use the word ‘an’ before it:
For this issue there are three situations:
=> In words:
1. When the first character of the word is consonant and is silent, then it takes the second character as the the initial sound and when such sound is initiated from a vowel then that word will be having the word “an” as the prefix.
> For example: in the word hour the, the first character "h" is silent, and the sound is initiating from the vowel "o", so the word ‘hour’ will have “an” as the prefix.
- Illustration: (Half an hour, be there in an hour)
- Examples: Heir, heiress, heirloom, honest, honesty, honor, honorable, hour, hourly, etc.
2. In abbreviations:
> whenever the consonants f, h, l, m, n, r, s and x comes as the first letter of an Abbreviation then that Abbreviation will have the word “an” before it. Because all these letters having "euh" as the initial sound when it is spelled separately.
o For Illustration: “an FBI officer”, “an NGO”, ……….
o Examples: FBI, HRM, HTML, LML, MOU, NGO, RDA, SC,
SJ, SP, SSP, STF, X-RAY
Abbreviations used as a word:
o When you use an abbreviation as a word then
the above rule is not applicable.
o For example: NATO, NASA, etc.