This essay offers some reflections about the crisis of the conception of the sources of the production of law, as elaborated in the tradition of legal positivism. After first briefly illustrating the historical and philosophical context that led to the focus on legislation and the formal view of the system of sources, the author then moves on to undertake an examination of the reality of contemporary legal orders, revealing this perspective's inadequacy. In particular, the crisis of the codes and the importance of the activity of creating law undertaken by the courts has resulted in other normative acts, which were not qualified as such by nineteenth century juspositivism, actually extending the range of sources. This process is illustrated with reference to the institution of negozio giuridico, whose significance in current criminal procedural law, administrative law and international commercial law is studied. Ultimately, the essay opines that the ability of an act or a fact to become a normative source no longer depends on criteria established in advance by the legislator, but on whether these acts and facts can be used by the judge to justify his decisions. The certainty of law can thus only be pursued by ensuring that the arguments employed in support of cases are correct.