Indefinite Article (a/an)

Indefinite Article

Form

There are two indefinite articles: a and an. An is used before words that start with a vowel sound, a, e, i, o, u. For example: an organisation, an effect, an accurate analysis.

A is used before words that do not start with a vowel sound. For example: a graph, a relationship, a model, a database.

Be careful, sometimes a word starts with a vowel, but it is not said with a vowel sound. This is common with words that start with the letter u but which have the sound y. For example: university, unit. For these words you need to use a: a university, a unit.

Use

The indefinite article, a or an, is used before singular nouns. It has a number of uses:

1. For the first time

A is used when you refer to something for the first time, so people do not know what it is.

Here’s an example:

It is sometimes called a trendline or a line of best fit.

In a graph, the independent variable is the x-axis (the horizontal line) and the dependent variable is the y-axis (the vertical line). You can see these labelled in the graph below.

Linear regression is a model used in data science.

We use a here because there is more than one model in data science. If linear regression was the ONLY model, you could say linear regression is the model used in data science.

Task 1

Here are some more examples from the reading passage. Can you work out why the indefinite article, a or an, has been used in each example?

You can download the answers here: Task 1 ANSWERS