This book aims to identify the sociological reasons that resulted in the perceived lack of authority of precedents in civil law systems, starting from the premise that common law systems rely on precedents, while civil law systems do not. The reasoning is based on the sociology of law, mainly on Max Weber’s theory, legal theory, and constitutional law. English common law, seen by Weber as a law devoid of formal rationality mainly because it does not allow for generalization and comprehensiveness, became a predictable system through stare decisis. This serves to highlight not only that it is not to be confused with common law but especially to clarify that “binding precedents” are necessary as the law moves away from calculability. The transformation of civil law due to the impact of constitutionalism, the increasingly widespread use of general clauses, and the evolution of the theory of interpretation eliminated the pretensions of logical positivism and, consequently, the predictability upon which it would be achievable. However, if the law contemplated by Weber ceased to exist and the new law came to depend largely on the subjectivity of the judge, this does not mean that society could remain helpless and devoid of guarantees of predictability and equality, as the new profile of civil law could not be compatible with a coherent legal order and a rational distribution of justice. In the end, the book seeks to demonstrate the fundamentality of precedent for the unity and development of law, clarity and generality, promotion of equality, institutional strengthening, limitation of state power, predictability, economic rationality, respect for the law, and increased personal responsibility.