The character of judicial opinions today as both formal and material sources of law was not an innovation brought about by the 1991 Constitution.This article proposes an operative definition of binding force, shows how the elements of that definition appear in judicial opinions, and presents the constitutionally appropriate meaning of the phrase "auxiliary criterion [criterio auxiliar]" in article 230 of the Constitution.Furthermore, this essay explains why when judges apply the law they are also making laws, in the form of norms contained in the reasoning of each opinion.Such norms, which should be called subordinate [adscritas], are binding for the high courts in a unique way.It is necessary to design a procedure to control how judges submit to the constitutional doctrine derived from judicial opinions; this procedure should include clear rules with which the Constitutional Court must also comply. IntroducciónEl derecho, como la cultura y en general todo lo que atañe al hombre, no es inmune al surgimiento, el cambio y el declive de modas y tendencias.El estudio de la historia de cualquier ámbito jurídico, e incluso de la propia teoría del derecho, revela bien la manera en que el llamado "espíritu d de los tiempos", el Zeitgeist, cala en las concepciones jurídicas vigentes, socava aquellas que le son incompatibles, las estigmatiza como arcaicas o en desuso, y las reemplaza por nuevas visiones que conviene poner a la vanguardia, en boga.