When to use 'a' and 'an'

English is a language of many eccentricities. The best way to learn English is to let oneself be charmed by it and take joy in its rich variety of expressions.
According to David Crystal, the renowned linguist, an average native speaker of English knows around 60,000 active and 70,000 passive words.

According to Purdue Online Writing Lab, “The choice of article is actually based upon the phonetic (sound) quality of the first letter in a word, not on the orthographic (written) representation of the letter.”

The article ‘an’ should be used before a vowel sound even if the first letter of the word (singular) is not a vowel.

For example:
•       An hour ago, an honest official, an FBI official, an MLA, an MP, an heir.
In the same way, the article ‘a’ should be used before a consonant sound even if the first letter of the word (singular) is not a consonant as in these examples:
•       A one-dollar book
•       In a country of the blind, a one-eyed man is the king.
The article ‘an’ should be used before unsounded ‘h’ if the sound that follows the article is a vowel.

Look at these examples: an honest student, for an hour,an honorable Member of Parliament.

The article ‘a’ should be used before words that begin with the letter ‘u’ when they sound like the ‘y’ in ‘youth’ or ‘young’. Here are some examples: a union, a unicorn. In the following words ‘h’ is pronounced and therefore, the article ‘a’ is used:

•       A hotel, a hymn, a historical novel

Sometimes no articles is used before certain nouns and this is called the ‘zero’ article.

Here are some rules for when not to use an article before a noun:

•       Don’t use articles before uncountable nouns, plural nouns and when talking about things in general: I don’t need advice from you. I don’t drink milk.

•       Don’t use articles before languages, countries, towns, streets, and single mountains: she speaks German.

In exclamations with what + uncountable noun: What wonderful news! What beautiful weather!