folie à deux

1 9.9

A rare mental illness where two people who are close, like partners or siblings, share the same false beliefs

noun
/fɔːˈliː ə ˈdɜː/

Specialized

: folie à deux

Psychiatrists have identified folie à deux as a psychiatric syndrome where two people share the same delusions.

Examples

In cases of folie à deux, two individuals may experience similar delusions as a result of their close relationship.
It's a shared disorder, called "folie à deux."

Intruders (2011)
Over a century ago, psychiatrists discovered this phenomenon and labeled it a folie à deux, or "folly of two."

Blog text (9)
According to Elst, from that point on, Khadija became a believer, and their relationship took on the character of a "folie à deux."

Academic text (2013)
When two friends believe they can read each other's thoughts, it may be a classic example of folie à deux.

Surface Forms

folie à deux singular

folies à deux plural

Morphology

folie + à + deux

This is a French loan literally composed as 'folie' (madness) + 'à' (of) + 'deux' (two), so a learner who knows the constituents can readily infer 'madness shared by two people.' Although it is a specialized clinical term used as a fixed expression in English, its meaning is directly compositional rather than idiomatic.

Etymology

The phrase folie à deux comes from French words folie ('madness') and deux ('two') and gives a clear image: two people so close that they share the same false belief. That's why it means 'a shared false belief' between two people.