Well, we all know some rules of English grammar. However, while writing we make numerous mistakes without even realizing that it is a mistake. In this article I wish to discuss some of the important rules of grammar pertaining to the usage of indefinite articles ‘a’ and ‘an’.

An indefinite article as defined in grammar-mosnter.com - The indefinite article is the word ‘a ‘or ‘an’. It is used before a noun to describe it as something non-specific. Let us look at the uses of the indefinite article along with incorrect uses and correct uses to know the difference in a better way.

A vowel comprises – a, e, i, o, u and rest of the English alphabets are consonants. However, certain words have a vowel sound, which may or may be start with a vowel. Similarly, certain words have a consonant sound, which may or may not start with a consonant.

A cat (starts with a consonant and has a consonant sound)

An egg (starts with a vowel and has a vowel sound)

Let us now look at the uses of indefinite articles in detail.

Rule 1: We need to use ‘an’ before a vowel sound and we need to use ‘a’ before a consonant sound. For example:

• A cat (a + consonant sound)
• An egg (an + vowel sound)

In most of the cases letters such as ‘o’, ‘e’, and ‘u’ as pronounced as vowels but at times they can and are pronounced as consonants. For example-

• A university (a + consonant sound though ‘u’ is a vowel)
• A one-way street (a + consonant sound though ‘o’ is a vowel)

Similarly,

• An English class (an + vowel sound, and ‘e’ is a vowel as well)
• An umbrella (an + vowel sound, and ‘u’ is a vowel as well)

Rule 2: Here, if a word starts with a consonant, but if the consonant letter is silent and is pronounced as vowel, we need to use ‘an’ but if the consonant is not silent, we use ‘a’ before such a word.

Let us look at the following usage and how it is correct or incorrect.

• It takes Meera about a hour to get dressed for any party. (This is an incorrect usage, since hour has a vowel sound even though ‘h’ is a consonant. Here ‘h’ is silent.)
• It takes Meera about an hour to get dressed for any party. (This is the correct usage, since ‘h’ is silent.)

Let us take a look at the second example.

• He had never been inside an hospital. (This is an incorrect usage, since hospital starts with a consonant and is pronounced as a consonant too. ‘H’ is not silent here, had it been silent, we could have used ‘an’ before the word hospital.)
• He had never been inside a hospital. (This is the correct usage. ‘H’ is not silent here.)

So, in short we use the same rule as above ‘a’ is used before a consonant sound and ‘an’ is used before vowel sounds.

• A hard-boiled egg (a + consonant sound)
• A huge building (a + consonant sound)
• An honest officer (an +vowel sound where ‘h’ is silent)
• An hour late (an +vowel sound where ‘h’ is silent)

Let us take a look at other words which begin with a silent ‘h’, they are:

Heir, honest, honor, hour, heirloom, honorary, hourly

Rule 3: We also need to use ‘an’ before an abbreviation or a letter which starts with a vowel sound and ‘a’ before an abbreviation or letter which starts with a consonant sound. For example, let us look at both the correct and the incorrect usage.

• Mohit is studying for ‘a’ M.A in English (Incorrect usage)
• Mohit is studying for ‘an’ M.A in English (Correct usage)
• I always prefer ‘a’ HB pencil (Incorrect usage)
• I always prefer ‘an’ HB pencil (Correct usage)
• She spelt the word with a ‘s’ instead of a ‘p’ (Incorrect usage)
• She spelt the word with an ‘s’ instead of a ‘p’ (Correct usage)

Here’s a list of letters that begin with a vowel sound, such as – A, E, F, H, I, L, M, N, O, R, S, and X. Barring these letters or alphabets, all other alphabets start with a consonant sound.

Examples of a + consonant sound

• A BSc 
• A VIP
• A bike
• A kite

Examples of a + vowel sound

• An MSc
• An elephant
• An egg plant
• An ox

Rule 4: We need to use ‘an’ before a number which starts with a vowel sound and use ‘a’ before a number which begins with a consonant sound. 

Let us take a look the examples below to understand this better:

• A three member panel (a + consonant sound)
• A twelve member jury (a + consonant sound)
• An eight seater golf cart (an + vowel sound)
• An eleven headed monster (an + vowel sound)

Rule 5: We need not use an/a before uncountable nouns. 

For example:

• She doesn’t like driving in a heavy traffic (Incorrect usage)
• She doesn’t like driving in heavy traffic (Correct usage)
• To teach young kids, you need a patience (Incorrect usage)
• To teach young kids, you need patience (Correct usage)

Rule 6: We need to use a/an when we mention something or someone for the first time.

Let us look at the following example.

• Geeta bought a new lamp shade. She asked her husband to take a look at a new lamp shade. (Incorrect usage)
• Geeta bought a new lamp shade. She asked her husband to take a look at the new lamp shade. (Correct usage)

Well, here we come to the end of few rules on the usage of indefinite article ‘a’ and ‘an’. I will be back with few more rules on the usage of the definite article ‘the’ in my next post.