25 Inconsistent behaviour

A particular aspect of the protection of reasonable reliance and expectations is to prevent a party, on whose conduct another party has reasonably acted in reliance, from adopting an inconsistent position and thereby frustrating the reliance of the other party. This principle is often expressed in the Latin formula venire contra factum proprium. The Principes directeurs express it as follows: ‘No party shall act inconsistently with any prior statements made by the party or behaviour on the part of the party, upon which the other party may legitimately have relied.’1. The Interim Outline Edition of the DCFR did not contain an express rule of this nature; it was thought that it could be arrived at by applying the general principles of good faith and fair dealing. Inspired by the Principes directeurs, the DCFR now incorporates an express provision which qualifies inconsistent behaviour as being contrary to good faith and fair dealing.2.