Un vs l'un - Lawless French Grammar


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Which one?

Do you know the difference between un and l’un? If you answer "Huh? Why would you ever put the definite article l’ in front of un?" then this lesson is for you.

There are two reasons to use l’ in front of un: one has to do with register, the other with euphony.

First things first: the word un has three potential roles:

When un is an article or a number, it’s always un: it cannot be replaced with l’un. So how do you know which role it’s playing? If un is followed by a noun, it’s either a number or an article. If it’s followed by anything else, such as the preposition de, it’s a pronoun, and may potentially be replaced with l’un.

Once you’ve determined that un is a pronoun, there are two reasons you might want to change it to l’un.

1) Formality

L’un is more formal than un, so using it makes your French sound more elegant.

Par exemple…

Vous devrez passer l’un de nos examens.		You’ll have to take one of our tests.
J’espère assister à l’une de vos conférences.		I hope to attend one of your conferences.

2) Euphony

At the beginning of a sentence or clause, it’s customary (though not required) to use l’un rather than un, because l’un just sounds better there. (see also on vs l’on)

Par exemple…

L’un de mes enfants est en retard.		One of my kids is late.
Oh là là, l’une d’entre elles a manqué le bus.		Oh dear, one of them missed the bus.

If the pronoun is plural, the definite article has to be plural as well: les uns, les unes. This is most commonly found paired with les autres.

Par exemple…

Les uns parlent, les autres écoutent.

Some talk, others listen.

Fixed expressions with l’un

c’est tout l’un tout l’autre – there’s no grey area, the situation is black and white
de deux choses l’une – there are two possibilities
l’un à l’autre – to each other
l’un après l’autre – one after the other
l’un dans l’autre – all in all
l’un d’eux, l’un d’entre eux – one of them
l’une d’elles, l’une d’entre elles – one of them
l’un et l’autre – both of them
l’un l’autre – one another, each other
l’un ou l’autre – either one, one or the other
ni l’un ni l’autre – neither one
soit l’un soit l’autre – either one, one or the other