What to know about the French phrase “Mais pourquoi”

Mais pourquoi is “But why” in French.

But why?  Let’s look at the words that make up Mais pourquoi, and how to use this phrase.

What does Mais pourquoi mean?

Mais pourquoi means “But why” in French.

As you may know already, mais usually means “but” and pourquoi means “why”.

This means that mais pourquoi can be translated into English word-for-word – something that’s always nice for us non-native speakers!

What’s the difference between pourquoi and mais pourquoi?

A cake sits on a cake presentation dish. It has sea green icing with mounds of bright pink icing lining the rim of its circular top. These pink mounds have colorful sprinkles scattered on them. There are also sprinkles all around the base of the cake.

Like “but”, mais can be used to show a contrary statement or to show emphasis. So, like the phrase “But why?” in English, mais pourquoi asks a question, adding some emphasis to it.

For instance, let’s look at the question Pourquoi as-tu acheté ce gâteau ? (Why did you buy this cake?)

This could simply be someone asking for information. If they used a certain intonation, of course, it might mean more -for instance, maybe they didn’t want you to buy this particular cake…or any cake at all (no fun!).

But if the person asked: Mais pourquoi as-tu acheté ce gâteau ? (But why did you buy this cake?) they’re clearly feeling some kind of strong emotion. Maybe they didn’t want you to buy it, or they’re confused as to why you bought it, for instance.

Here are some other example sentences with mais pourquoi:

Mais pourquoi l’as-tu invité ? (But why did you invite him?)

Mais pourquoi faire ça à minuit ? (But why do/why are you doing this at midnight?)

Mais pourquoi c’est toujours à moi de faire le ménage ? (But why am I the one who always has to do the housework?)

Like “But why”, mais pourquoi can also be used on its own. For instance:

On va rendre visite à la tante Sylvie. – Mais pourquoi ? (“We’re going to visit Aunt Sylvie.” “But why?”)

Elle a dit de sortir la poubelle ce soir au lieu de demain matin.Mais pourquoi ? (“She said to take out the garbage tonight instead of tomorrow morning.” “But why?”)

C’est lui que j’aime ! – Mais pourquoi ? (“He’s the one I love!” “But why?”)

Note that using mais pourquoi on its own is a bit less common in French than using “But why” on its own is in English.

You might also see mais pourquoi preceded by a filler word or a short reply – for example:

Oui, mais pourquoi ? (Yes, but why?)

Ah bon? Mais pourquoi ? (Oh? But why?)

This would be most often be in spoken everyday French, rather than written French.

Is mais pourquoi formal or informal?

Two women, seen from behind, sit in green metal lounge chairs at one of the fountains in the Jardin des Tuileries. They are both reading paperback books and have taken their shoes off. Each one has suitcases beside her chair.

Mais pourquoi tends to be used in informal contexts. Because mais is used in a way that shows emotion, it could be seen as impolite if used in formal contexts or with a stranger. The same could be said for “but why”.

For instance, if you met someone who told you J’aime les chiens (I like dogs), and you asked Mais pourquoi ? (But why?) it would seem like you found their statement totally puzzling or ridiculous. Better to keep it neutral and simply ask something like Pourquoi aimez-vous les chiens ? 

That said, mais pourquoi can be somewhat neutral or formal when when it’s used in a phrase, rather than as a standalone expression or reply. (Note that these questions would also have to be general or not directly addressed to the speaker, rather than directly addressing something like a person’s opinion. Mais pourquoi aimez-vous les chiens ? would still be pretty rude to ask someone you’d just met, for instance.)

Here are some examples of how to use mais pourquoi more politely:

Mais pourquoi fonder un musée de l’Art nouveau ? (But why found/create an Art Nouveau museum?)

Mais pourquoi avez-vous choisi de partir vivre à l’étranger ? (But why did you choose to live abroad?)

versus the less polite way:

Il a fondé un musée de l’Art nouveau ? Mais pourquoi ? (“He founded/created an Art Nouveau museum?” “But why?”)

Elles sont parties vivre à l’étranger. – Mais pourquoi ? (“They left to go live abroad.” “But why?”)

Interestingly, you can see mais pourquoi used in a neutral or polite way versus an informal or rude way, just by inputting it into an online search. The results that come up run the gamut from news segment titles to funny YouTube videos.

Is there another way to say Mais pourquoi?

If you look for a synonym for mais pourquoi, you may come across the phrase Pourquoi donc?  Pourquoi donc is a rough equivalent, but it really means “So why”.

For instance: Tu savais que j’avais besoin de dormir. Pourquoi donc m’as tu réveillé ? (You knew that I needed to sleep. So why did you wake me up?)

Donc is also less commonly used in general than mais, and overall the phrase pourquoi donc is a bit more formal than mais pourquoi, so it’s not an exact match.

Another option for a synonym for mais pourquoi could be Et pourquoi ? (And why?), although this is usually used more as an emphasized question following a list – say, a list of grievances or things a person didn’t like in a movie. Ex: Et pourquoi le chat se transforme en sirène à la fin ? (And why does the cat transform into a mermaid at the end?)

Should I use mais pourquoi?

As a general rule, it’s probably better to just use pourquoi on its own if you want to ask “Why”. Pourquoi on its own will always be more neutral and often more formal, making it the better choice in most situations. If you opt to use mais pourquoi, be sure it’s in a question where you want to emphasize an emotion like frustration, anger, surprise, or curiosity.


I hope this article has helped you better understand mais pourquoi. If you’re wondering how to practice using this phrase, reading, writing, and listening to French is a good way to start. And so is using the French Together app, which will give you lots of practice with everyday French conversations and phrases.

With practice, you’ll never have to think, Mais pourquoi ? when you see the phrase mais pourquoi!

Must reads

  1. What are the best French learning apps in 2024?
  2. The 16 best websites and apps for French conversation practice
  3. Duolingo French review: The good, the bad and the ugly

Alysa Salzberg

Alysa Salzberg is an American writer, worrier, teacher, and cookie enthusiast who has lived in Paris, France, for more than a decade. She has taught English and French for more than ten years, most notably as an assistante de langue vivante for L'Education Nationale. She recently published her first novel, Hearts at Dawn, a "Beauty and the Beast" retelling that takes place during the 1870 Siege of Paris. You can read about her adventures here, or feel free to stop by her website.