Abstract: Impossible to break down, does simplicity lend itself to description ? This contribution demonstrates how, in Un cœur simple, Flaubert deploys a poetics of simplicity which fuses with the simplicity of the character, Félicité, in order to give a form to a singular experience of belief which distances itself as much from stupidity as from hagiography. Simplicity proves particularly effective at countering the aestheticisation of the simple life, of the “simple”.