The absence of reasons given for decisions, which is one of the main characteristics of Ancien Regime justice, is generally inferred from the interdiction made by the royal decrees since the 14th century to disclose the secrets of deliberations. But can one really establish a causal link between them ? In fact, no royal decree or any other normative prescription explicitly forbade the judges of Parliament to give the reasons for their judgments. The author of the Style de la chambre des enquêtes only advised the judges against the practice of disclosing the reasons for their decisions. The Style thus adopted the warnings repeated by the Decretalists since the early years of the 13th century. Therefore, not revealing the rationes decidendi appears to be a common use rather than a firm principle of ancient French law. That use had been imposed by Parliament : first because it was a guarantee for the independence of its members, afterwards - and mainly - because it ensured the courts great liberty, especially because it allowed judges to find a solution outside the formal legal sources. It is because of these reasons - despite the fact that the absence of ratio decidendi constituted a major obstacle to the assertion of a "jurisprudence of the sovereign courts" - that the use persisted until the Revolution.