This French expression doesn’t literally mean putting your hand in actual fire…
Why do I need to know mettre sa main au feu?
This French expression is commonly used when someone is 100 percent sure about something.
What does it mean?
The expression mettre sa main au feu, roughly pronounced metr sah mein oh fuh (listen here) literally translates to “to put one’s hand in the fire”.
It really means “to be absolutely certain about something” or “to swear something is true”.
This expression dates back to the Middle Ages, specifically a practice known as “trial by ordeal” (l’ordalie). When someone wanted to prove their innocence, they could choose to undergo a form of torture as proof of their good faith through God. The idea was to complete an impossible test, unless God intervened by preventing suffering, thereby allowing the person to prove their innocence.
Among these trials, the best-known involved grasping a red-hot iron bar and holding it for a few moments without being burned. Others walked on hot coals, and some even went as far as duelling.
This practice thankfully forms no part of the modern French judicial system – but the expression remains.
Use it like this
Je mets ma main au feu, c’est lui le coupable. – I’m absolutely certain he’s guilty.
Franchement, je mets ma main au feu que tu te trompes. – Honestly, I swear I think you’re wrong.
Ne jamais mettre sa main au feu pour l’autre. – Never vouch for someone else absolutely.
