CS Sealey

New Zealand-based sub-editor, writer and author

When to use ‘a’ and when to use ‘an’

Is it a or an?

I know. You must be thinking, ‘Surely, this is one of the few easy things about the English Language!’

When I was in primary school and first learning about grammar and which end of the pencil to use, I remember my teacher telling us all that words beginning with vowels (a, e, i, o and u) should be preceded by an rather than a. This was very easy to remember. However, it did not remain so very easy.

Both a and an are types of word called determiners, just like the, every, one and some. A determiner is a modifying word that expresses the kind of reference a noun possesses in a particular context. In layman’s terms, a determiner determines whether the noun in question is plural, whether it belongs to a certain person or thing and whether it is the specific object in question.

But I don’t intend to go into the more complex determiners today. Let’s tackle a and an.

There was a cat on the doorstep.

The boy tossed an orange into the air.

These two examples adhere to the simple an and vowels rule. Cat begins with a consonant, so it is preceded by a rather than an; while orange begins with a vowel, so it rightly has an an in front of it.

This is the point where someone will put up their hand and ask about the letter ‘H’.

H words

‘H’ is an interesting letter because it is quite often silent or not pronounced. Words that begin with the silent ‘H’ should be preceded with an an.

The storm raged for an hour.

My uncle was an honorary member of the local council.

He was an honest sort of chap.

This makes sense, because the silent ‘H’ can be considered a vowel. But what happens when the ‘H’ is pronounced? Do we precede words such as holiday, habitat, home and hangar with an as well?

It depends.

Though some will insist on preceding all ‘H’ words with an, this is one of those ‘rules’ in English that is evolving. With the trend towards modernisation, I predict that all aspirated-H words will be commonly preceded with a.

A holiday in Rome would be nice.

This is a habitat currently in danger of industrialisation.

A hangar is not something to put your clothes on.

I personally do not put an in front of my aspirated-H words when I’m writing, simply for the fact that I would rather not sound pompous and dated.

Now, what about in spoken English? Sometimes, when we’re in a hurry, getting lazy or simply speaking with one of our many accents, we sling our words together and often miss the ‘H’ in our aspirated-H words, such as:

‘I went to see an historic movie yesterday.’

May sound like this.

‘I went to see an ‘istoric movie yesterday.’

As opposed to:

‘I went to see a history movie yesterday.’

This is partly to do with accents and also partly to do with inflection, as the word historic (his-TOR-ic) has a different inflection than history (HIST-ory).

So the verdict on ‘H’ words is a mixed one. In writing and the spoken word, using an for aspirated-H words is increasingly seen as dated or scholarly, while silent-H words are widely accepted as honorary vowel words and so a is adopted.

U words

‘Wait, isn’t that a vowel word? There should be no exceptions here!’

Sorry, there are. Similarly with the above dilemma with aspirated vs silent-H words, some ‘U’ words sound like they begin with a ‘Y’, such as unicorn, university and unilateral. These words are usually preceded by a rather than an, even in writing.

I completed a university degree that lasted three years.

‘To have a unicorn for a pet would be… interesting.

Compare these with regular ‘U’ words.

It was an unfortunate incident that drove the two together.

‘This is such an under-rated album.’

As you can see, the regular ‘U’ words adopt the usual vowel and an rule. This is the same in spoken English; however, the speaker usually does this without thinking (which is handy). So while the vowel and an rule, in most cases, is still a rule you can follow with ‘U’ words, there are exceptions. (Where would the English Language be without those?)


This one is also slightly tricky.

An abbreviation is when a noun is shortened usually using the first letters of each word, such as HTML (hypertext markup language) or FBI (Federal Bureau of Investigation). Whether an abbreviation should be preceded by an or a depends on how you say it, not which letters are used.

The two examples of abbreviations above are initialisms; namely, the way they are said is H-T-M-L and F-B-I. In a sentence, they would be expressed like this:

‘This is an HTML document.’

An FBI officer sprinted along the street.

Note that, even though FBI begins with ‘F’—a consonant—it is preceded with an. This is because ‘F’ is pronounced as ‘eff’—a vowel sound. Just like with the silent-H words, it goes on what it sounds like, not what letter it is.

Other examples are:

An RMS car licence

An ABC programme

An NYPD police vehicle

A UK ministerial official

As above, it depends how the letters sound when spoken. ‘R’ (ar), ‘A’ (ay) and ‘N’ (en), when spoken out, begin with vowels; but, interestingly, ‘U’ (yoo), when spoken out, begins with a consonant!

Acronyms are easier to determine because, though they are also abbreviations, they have moved beyond the initialism stage and become words; therefore, they are treated as such with all the above rules regarding an and a.

A NASA space mission

An OPEC summit

A PIN number

An HIV patient

Note that ‘H’ is pronounced ‘aych’ (vowel sound) rather than ‘haych’ (consonant); therefore, HIV is preceded by an, not a.

In conclusion, determining when to use an and when to use a mostly comes down to what sounds best. After all, languages were first spoken before they were written or read, so trust what feels right on your tongue—you will probably be right!

Good luck!

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