French Civil Code

Error, fraud and violence vitiate consent when they are of such a nature that, without them, one of the parties would not have contracted or would have contracted on substantially different terms. Their decisive character is assessed having regard to the persons and circumstances in which the consent was given.

Vices of consent are a cause of relative nullity of the contract.

An error of law or of fact, unless inexcusable, is a ground for nullity of the contract where it relates to the essential qualities of the service due or to those of the other contracting party.

The essential qualities of the performance are those which have been expressly or tacitly agreed and in consideration of which the parties have contracted. Error is a cause of nullity whether it relates to the performance of one party or the other. Acceptance of a hazard as to a quality of the performance excludes error relating to that quality.

Mistake as to the essential qualities of the co-contractor is a ground of nullity only in contracts concluded in consideration of the person.

A mistake as to a mere motive, extraneous to the essential qualities of the performance due or of the co-contractor, is not a ground of nullity, unless the parties have expressly made it a decisive element of their consent. Nevertheless, a mistake as to the reason for a liberality, in the absence of which its author would not have disposed, is a cause of nullity.