The paper focuses on some legal processes that have affected the principle of legal certainty in the sphere of private law and have given a new crucial role to interpretation and argumentation. Within the legal orders the interpreter has taken over the legislator as a subject in charge for the warrantee of legal certainty. This undermined the systematic nature of the civil code through a process of slow de-codification. The shift from the abstract rule to the general clauses, from the mechanical application of the law according to the deductive paradigm to the acknowledgment of the importance of the context of application for understanding the norm has contributed to a renovated role of the judicial interpretation. Finally, in face of the changing of the regulatory landscape with the rise and spread of forms of transnational as well as soft law and the consolidation of the Community law, the principle of legal certainty should be conceived without embracing either nihilism or formalism.