Indefinite Articles: 'A' or 'An'? | Mastering Grammar

(Last Updated: 11 February 2024)

TL;DR: Use a before words that start with a consonant sound and an before words that start with a vowel sound. It is important to note that a word starting with a vowel letter does not necessarily begin with a vowel sound, and likewise, a word beginning with a consonant letter may not always start with a consonant sound.

Using Indefinite Articles A and An Correctly in English

In English, a and an are indefinite articles used before a singular countable noun to indicate that the noun is not specific but rather one of many.

While it is commonly believed that an is used before words starting with A, E, I, O, or U, and a is used before words starting with the other letters, there are many exceptions to this 'rule'.

(Source: Pan Lloyds 26-Week English Consolidation Practice: Grammar (1B))

The actual rule is this: use a before words that start with a consonant sound, and an before those that start with a vowel sound.

Understanding Vowel Sounds and Consonant Sounds

To choose between a and an correctly, it is essential to distinguish between a vowel letter and a vowel sound.

English has five vowel letters: A, E, I, O, and U. The remaining letters are consonant letters.

When it comes to vowel sounds, there are generally considered to be 20, although the exact number depends on the speaker's dialect or accent. The remaining 24 sounds (e.g. /b/, /k/, /f/, and /m/) are consonant sounds.

So how can we tell the difference between a vowel sound and a consonant sound? To put it simply, a vowel sound is one that can be made with little or no obstruction to the airflow in the vocal tract. For instance, the word apple begins with the vowel sound /æ/ made with the mouth open and the tongue relaxed. When we make the /æ/ sound, there is virtually no obstruction to the airflow from the lungs to the mouth.

In contrast, a consonant sound is made with some degree of obstruction to the airflow at various points in the vocal tract, such as the lips, teeth, tongue, or glottis. For example, the word pie begins with the consonant sound /p/. To produce the /p/ sound, you need to close your lips to build up pressure in your mouth, and then release the air by opening your lips. The airflow is obstructed at the lips during the closure phase.

Examples of Correct Usage: A and An

Consider the letter F (/ef/). If you say the letter out loud a few times, focusing on its sound, and compare it with words such as egg (/eɡ/) and elephant (el.ɪ.fənt/), you will quickly realise that they all begin with the same vowel sound /e/. Even though F is a consonant letter, it begins with a vowel sound. Therefore, the correct indefinite article to use before F is an, not a:

John got an F in the test. 
John got a F in the test.

His dream is to become an FBI agent. (FBI: efbiːˈaɪ/)
❌ His dream is to become a FBI agent.

As demonstrated, the choice of a or an depends on the initial sound of the following letter or word. Consider the following examples:

This is a one-way street. 
This is an one-way street.
(One (/wʌn/) begins with the same consonant sound /w/ as the initial sound in words like win (/wɪn/) and wood (/wʊd/).)

Have you ever seen a UFO before? 
Have you ever seen an UFO before?
(UFO is usually pronounced by saying each letter individually (i.e. 'you-ef-oh'). The letter U (/juː/) begins with the same consonant sound /j/ as the initial sound in words like yellow (jeləʊ/) and yes (/jes/).)

✅ There is an MTR station near our office. 
There is a MTR station near our office.
(The abbreviation MTR stands for Mass Transit Railway, which is the train system in Hong Kong. The abbreviation is pronounced by saying each letter individually (i.e. 'em-tee-are'). Similar to F (/ef/), which we saw earlier, M (/em/) also begins with the same vowel sound /e/ as the initial sound in words like egg (/eɡ/) and elephant (el.ɪ.fənt/).)

Yao Ming became an NBA player in 2002. 
Yao Ming became a NBA player in 2002.
(Like F (/ef/) and M (/em/), N (/en/) also begins with the vowel sound /e/.)

Anna is an honest girl. 
Anna is a honest girl.
(Although the word honest (ɒnɪst/) begins with the consonant letter h, its initial sound is actually a vowel sound (i.e. /ɒ/), because the h in honest is silent.)

From these examples, it is clear that a word beginning with a vowel letter (e.g. one) does not always start with a vowel sound, and similarly, a word beginning with a consonant letter (e.g. honest) may not start with a consonant sound.

In summary, to use a or an correctly, focus on the initial sound of the following word, not just the first letter.

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Examples from the Media

A high-profile report out of B.C. recently concluded a universal basic income was not the best strategy for poverty reduction. —Toronto Star (2021)

An RNA therapy called inclisiran interferes with RNA to limit the production of a protein that can increase 'bad' cholesterol levels. —Daily Mail (2022)

The collision Saturday was caught on Reeves's camera, and the startling footage of an SUV barreling toward the podcast recording went viral on social media. —The Washington Post (2023)

Dr Wriedt estimated that radiologists would charge patients between $54 and $101 up-front for an X-ray if they factored in the lost bulk-billing incentive. —The Sydney Morning Herald (2016)


Choose the correct article to complete each sentence.

1. The driver made a/an U-turn and sped away.

2. My brother is a/an university student.

3. I always carry a/an umbrella in my bag in case it rains.

4. Using a tranquilliser dart is a/an easy way to immobilise a dangerous tiger.

5. Is London a/an European city?

6. Chris is a/an honourable man.

7. Every time I go to work, I walk past a/an house that has a beautiful garden in front.

8. Anna bought a/an one-bedroom apartment in Toronto.

9. A/An open field is the perfect place to play football.

10. If you take a bus, it may take a/an long time to reach your destination, but it can also be a relaxing and scenic way to travel.

11. This house features a/an L-shaped kitchen layout.

12. Hey, there's a/an R written on the wall. Do you know what it means?

Answer Key

1. a    2. a    3. an    4. an    5. a    6. an    7. a    8. a    9. An    10. a    11. an    12. an

Real-World Examples of Misuse

The word persuasive starts with a consonant sound, specifically /p/. Hence, we use a instead of an before it. Saying an persuasive way is incorrect, as an is used before vowel sounds only.
(Source: HKDSE English Language 2015: Examination Report and Question Papers)
(Also by HKEAA: 1/2/3/4/5/6/7/8/9/10/11/12/13)

1. As a verb, access is transitive and therefore takes a direct object.
2. Despite starting with a vowel letter, the word user actually begins with a consonant sound. Therefore, it requires the indefinite article a preceding it.
(Source: Hong Kong Examinations and Assessment Authority)
(Also by HKEAA: 1/2/3/4/5/6/7/8/9/10/11/12/13)

Even though SMS starts with a consonant letter, its pronunciation begins with a vowel sound ('ess'). Therefore, we say an SMS instead of a SMS.
(Source: HKEAA Online Bookstore)
(Also by HKEAA: 1/2/3/4/5/6/7/8/9/10/11/12/13)

Since SPCCPS is pronounced as an initialism (i.e. ess-pee-see-see-pee-ess), and the first sound is a vowel sound, the correct indefinite article to use is an instead of a.
(Source: St. Paul's Co-educational College Primary School)
(Also by the Same School: 1/2/3)

1. The indefinite article an should be used before MTR Complimentary Annual Pass because the initialism MTR starts with a vowel sound. The choice between a and an is determined by the sound of the following word, not the spelling. Since MTR is pronounced 'em-tee-are', which begins with a vowel sound, an is the correct article to use.
2. Starting a sentence with a numeral is generally not considered good practice in formal writing. Instead, it is recommended that the number be spelt out or the sentence be rephrased to avoid this issue. One possible solution in this case would be to add the phrase A total of to the beginning of the sentence.

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