Abstract
The point of this thesis is to question the existence of a real difference between the notion of good faith and that of loyalty. I was brought to this topic by noticing the alternative use of words such as good faith and loyalty in the contractual field. This misunderstanding was maintained by judges as well as by a consequent part of the doctrine. Might such notions merge into the same idea so that they’d be used in the same situations to regulate the same behavior ? Stating that it cannot be, the aim of this thesis is to prove the necessity of clearly separing these two notions which are doomed by their lexical proximity and their poor definition to be mistaken for one another. The consequent purpose of this thesis is to preserve the very principle of legal security.Therefore, the following study aims at establishing criteria of distinction between good faith and loyalty when it comes to contract law, as they do not endorse the same role. While good faith is a general and minimal behavioral norm that applies to any contractual relationship, loyalty is a special and demanding standard. Also, this difference in nature will induce a difference of scope and regime allowing to preserve the subject of law from the unfortunate practical consequences that may be caused by the confusion of these notions.