摘要：Checks the present study the legal and social effectiveness of the principle of ability to pay and its application to taxes in general from a critical-descriptive analysis, through doctrinal research. A sense of historical development as well as their social and economic contexts of each phase of humanity, to the contemporary era, shows that the law, in general, has always had in its evolutionary process, the observance of moral and ethical values which underlie and support the basic core of legal principles. Addresses is also the social and fiscal justice and its link with the principle of ability to pay, using the theoretical framework seen in John Rawls and Hans Kelsen. It is observed, also, the Italian doctrine regarding the principle on screen and subjective theories that analyze the guiding personal aspects of the phenomenon of tax levy. Analyzes other fundamental principles and immunities, remissions and especially tax exemptions, emphasizing the "least free" as limiting institutes the power to tax in order to verify its impact on the legal and social effectiveness of the principle. Such studies aim to also investigate the issue of constitutional principles and norms and values, especially the principle of ability to pay and their respective applications to taxes, fees and improved contributions. Finally, it exposes the social efficacy of ability.
关键词：Justiça social e fiscal;Princípios constitucionais tributários;Capacidade contributiva;Exonerações fiscais;Tributos.
