This is a paper about the nature of the reasons that the United States Supreme Court uses to resolve cases involving freedom of speech. I believe that there are two types of reasons that guide the First Amendment decision-making process: formal and substantive. Substantive reasons are those that law shares with other domains of human social action, such as morality, economics and politics. Formal reasons, in turn, are authoritative legal reasons - in the sense that they derive from a valid legal norm (Constitution, laws, regulations, precedents, contracts, and other related normative documents) - and compulsory (or exclusionary), because they generally exclude competing substantive reasons from the horizon of decisional reasoning. My aim in this dissertation is to describe the way in which formal legal reasoning and substantive legal reasoning have to some extent been reconciled at the heart of the decision-making practice of the US Supreme Court. To this end, I endeavor to present, comment on and compare with each other some of the most emblematic judgments carried out by the Court over more than a century of First Amendment constitutional jurisdiction. I also try to show that the adjudicatory methods she has developed can be classified according to the importance each of them attaches to the formal reasons (or, on the other hand, the substantial reasons) for freedom of discourse. For example: the conflict between balancing and the methodologies belonging to the definitional tradition (e.g., absolutism, categorization) represents nothing more than a particular instance of the more general conflict between form and substance in American legal thought. But while until the mid-1960s the discussion about methods of deciding freedom of speech was completely dominated by the opposition between balancing and absolutism, little by little the United States Supreme Court, in company with the great names of legal thought in that country, opened its eyes to the existence of middle points between those two extremes. The result was the creation of new normative theories of decision (e.g., definitional balancing), as well as a series of tests, formulas, parameters and presumptions, thus making it possible for formal and substantive elements of First Amendment legal reasoning to coexist in the realm of the same decision-making methodologies. Beyond my effort to rationally reconstruct the transformations that the Supreme Court s methodological approaches have undergone over the last few decades, I also propose to give them some meaning. I argue that the Court s historical concern with the stabilization of its decision-making procedures, as well as with the predictability of its judgments, is closely related to the belief that the justifications underlying the First Amendment (e.g., greater control of government by the people; the search for truth; and artistic and intellectual self-expression) are most effectively promoted by adopting a decision-making approach that prioritizes the achievement of better outcomes on a global level over what often appears to be the best outcome for the most immediate case.