4. The indefinite article and ‘one’

There are situations where the indefinite article clearly has an idea of 'one', in particular in the numbers 'a hundred', 'a thousand', 'a million', 'a dozen', and so on, when they are alone or followed by a noun.

Johnny has at least fifty, worth over a hundred dollars each.

It lasted a thousand years.

In these examples you could replace a with 'one' with little difference in meaning, although 'one' is more emphatic. This is also true of words which refer to standard measurements.

It seemed more like an hour.

I owe it all to a pound of dog meat.

He poured an inch of beer into my glass.

Note the following points:

• When numbers are written as figures, the indefinite article is not included, so you write '100', '1000', but you say: 'a hundred', 'a thousand' or 'one hundred', 'one thousand'. When the figure 1 refers to 100 but is not the first part of the number, then you must say it as 'one': '2100' must be said as 'two thousand, one hundred'. Again, when saying a number between 1100 and 1999, you say 'one', not 'a': '1400' must be said as 'one thousand, four hundred'.

• You cannot use 'one' for emphasis in idiomatic expressions such as 'ninety-nine times out of a hundred' (ie 'nearly always') and 'a thousand times' (ie 'very many times'). These expressions are fixed.

• 'One' must be used when using two words referring to measurements, for example 'foot' and 'inch': 'It's one foot ten inches long'. When using just one word referring to a measurement, you use a unless you want to show you are being precise: 'It's a foot long'.

• Both the indefinite article and 'one' can be used with most fractions, but the indefinite article is more usual: 'a tenth' or 'one tenth,' 'a quarter' or 'one quarter'. 'One' is rarely used with 'half', and in an expression like 'half an hour', 'one' is not possible.

As stated above, you normally use a, not 'one', when mentioning something for the first time. 'One' is only used before nouns in the following ways:

• when being precise or emphasizing that only one thing is involved

I have two younger brothers and one sister.

I've only got one room, but there's a Couch.

One look at Mopani clearly showed him that such an approach would not do.

She was hopping on one foot.

Note that 'one more' is an emphatic way of saying 'another'.

I think he should be given one more chance.

• when contrasting one thing in a pair or a group with another

I went off with a bottle under one arm and some extra diapers under the other.

Note that 'one' can be used as a pronoun in a noun group beginning with the indefinite article. The noun group must have an adjective in it. You use a noun group like this when referring to

something of the same kind as what you have just been talking about.

'The cage is too small.’ - 'We're going to make a bigger one.'

5. Expressing rates

The indefinite article is used between two noun groups to express a rate or ratio. You can talk about prices, salaries, and speeds in this way.

...as fast as 500 kilometres an hour.

...rising by 1 per cent a year:

...a thousand pounds a week.

She worked 14 hours a day.

This construction can also express the frequency with which something happens, using 'once', 'twice', 'three times', and so on.

Kate visited him daily, sometimes twice a day.

You can express a similar idea more emphatically with 'each' or 'every'. In more formal or technical contexts, 'per' is often used.

Approximately 10 per cent of households move each year.

...twenty or thirty times every second.

At the end of 1973 membership fees were raised to 25p per month per head (three pounds per year).

Note that it is also possible to use the in rates denoting prices, but this is very rare.

Petrol costs around three pounds the gallon.