Which one should you use?
While tu es fou ? is a standard way to express this, you can make the question more explicit and standard by adding est-ce que to the beginning of the sentence: est-ce que tu es fou ?
Is there a formal and an informal way to say it?
If you want to ask if someone is mad in the sense of being angry, you can use the formal Êtes-vous en colère ? or Êtes-vous fâché(e) ? In an informal setting with friends or family, you can use Tu es fâché(e) ? To ask if someone is mad specifically at you in a casual and intimate setting, use Tu m'en veux ? For a more colloquial and slangy way to say someone is acting crazy or irrational, you can use t'es dingue ?
How does it change in a sentence?
The adjective changes to the feminine form folle in tu es folle ? if you are addressing a woman. Use the form vous êtes fou ? to ask the question in a formal setting or when addressing more than one person.
Did you know?
- One origin of fou is linked to the Arabic word for 'elephant', which referred to the bishop piece in chess and eventually to court jesters.
- In very casual speech, the pronoun tu is often shortened to t' as in t'es fou ?, effectively merging the subject and the verb.
Examples in context
- Attends, tu es fou ?Wait, are you mad?
Sources
- Word origins: Wiktionary entries fou, tu, CC BY-SA 4.0.
