'Devoir' vs 'avoir besoin de' - What's the Difference?

The word ‘to need’ has two common translations in French: devoir and avoir besoin de. The best translation of Devoir is perhaps as 'to have to', while avoir besoin de translates more closely as 'to have need of'. Even if you're a total beginner, you’ve probably come across these two ways of expressing necessity already, as they’re extremely common. And you might be wondering what – if anything – is the difference between them.

The distinction is quite simple. In fact, most of the time, devoir and avoir besoin de can be used interchangeably. For example, in the following sentences:

'Vous devrez/aurez besoin de lire ces manuels avant l'examen.'

'You will need to read these textbooks before the exam.'

'Le facteur doit/a besoin de terminer sa tournée avant 3 heures.'

'The postman needs to finish his shift before 3 o'clock.'

'Je dois acheter / J'ai besoin d'acheter de nouvelles chaussures.'

'I need to buy some new shoes.'

Notice that in each of these sentences, the term in question is followed by an infinitive verb. When you're expressing a necessity to 'do something' in this way, you can use both devoir and avoir besoin de. Just remember that, in the case of the later, avoir is the part of the phrase that needs to be conjugated.

So far, so simple. But avoir besoin de can also be followed by a noun, as in the following examples.

'J'ai besoin d'une nouvelle coupe de cheveux.'

'I need/have need of a new haircut.'

'Ils auront besoin d'un plan de secours.'

'They'll need/have need of a backup plan.'

'Je pense que tu as besoin de nouveaux amis.'

'I think you need new friends.'

What's important to note here is that you cannot use devoir in any of these examples, i.e. when referring to a noun. A sentence like 'Je dois une pomme' would not make sense in French (although 'J'ai besoin d'une pomme' would, assuming you ever needed an apple). If it helps, you might want to think of devoir as equivalent to 'to have to' in English, rather than 'to need'.

On the other hand, devoir has another meaning. You may have come across this word in a context where it means 'to owe'. Don't let this confuse you. It's the same verb, and conjugates exactly the same way. The difference is that, while devoir, meaning 'to need', is intransitive, this form of the word is 'transitive' – in other words, it takes a direct object, as in the following example.

'Tu me dois vingt euros.'

'You owe me twenty Euros.'