Article 31.1 of the Spanish Constitution: "Everyone will contribute to the support of public expenses in accordance with their economic capacity through a fair tax system inspired by the principles of equality and progressivity that, in no case, will have a confiscatory scope."

Contributing through taxes to the support of public expenses could simply be a moral duty of the citizen; However, our Constitution in the reproduced article 31.1 elevates it to the category of legal duty. It is thus part of the Citizen Statute, made up of fundamental rights, public freedoms, rights and duties. The statement of Title I, to which the aforementioned article belongs, attributes the fundamental character of both the rights and duties contained therein.

The existence of rights and duties of citizens makes it necessary to integrate them and weigh the interests at stake whenever a conflict may occur between them. No right is absolutely superior and preeminent, nor are any of the duties; Case-by-case analysis and weighing in its application is legally correct. Along these lines, various rulings from both the TC and the CJEU confirm this approach:

Judgment of TC nº 110/1984, of November 26, FJ 3, weighing the duty to contribute and the right to privacy of citizens : " to what extent can the Administration demand data relating to the economic situation of a taxpayer? There is no doubt that in principle it can do so. The simple existence of the tax system and the inspection and verification activity that Its effectiveness demonstrates this. It is also clear that this right has firm constitutional support in Article 31.1 of the Fundamental Norm, according to which "everyone will contribute to the support of public expenses in accordance with their economic capacity through a fair tax system." inspired by the principles of equality and progressivity that in no case will have a confiscatory nature." And it seems useless to remember that in today's world the breadth and complexity of the functions assumed by the State means that public expenses are so large that the duty of An equitable contribution to its support is especially pressing. Otherwise, an unfair distribution of the tax burden would occur, since what some do not pay when they should pay, others with more civic spirit or with fewer possibilities of defrauding will have to pay. Hence the need for a particularly vigilant and effective inspection activity, although it may sometimes be uncomfortable and annoying."

Sentence of TC nº 76/1990 of April 26, FJ 3: " This constitutional reception of the duty to contribute to the support of public expenses according to the economic capacity of each taxpayer forms a mandate that binds both public powers and citizens and affects the very nature of the tax relationship. For citizens, this constitutional duty implies, beyond the generic submission to the Constitution and the rest of the legal system that Article 9.1 of the fundamental norm imposes, a situation of subjection and collaboration with the Tax Administration in order to support public expenses whose indisputable and essential public interest justifies the imposition of legal limitations "to the exercise of individual rights. For public powers, this constitutional duty also entails specific demands and powers in order to ensure the effectiveness of its compliance by taxpayers."

Judgment of TC nº 50/1995 of February 23, FJ 6, when weighing the duty to contribute and the right to the inviolability of the home: " On the other hand, the general interest inherent in the inspection activity of the public treasury is vital in a democratic society for the economic well-being of the country, as provided for in the Rome Convention when legitimize the interference of public authority in the right to respect for private and family life, home and correspondence of any person (art. 8.1 and 2), in the light of which fundamental rights and their exceptions must be interpreted (STC 114/1984), without prejudice, on the other hand, to the margin of appreciation left to the prudent discretion, not arbitrariness, of each State to configure these measures (STEDH, Riema case, Sentence April 22, 1992). time to lift public charges in accordance with economic capacity and within a fair tax system, is proclaimed in art. 31 of the Constitution and entails, with the generality of the imposition, the proscription of tax fraud, as one of the most pernicious and reprehensible forms of lack of solidarity in a democratic system, as evidenced by the legislation in this regard in the countries of our country. geographical and cultural environment."

 (Fundaments are those of the previous rulings also included in the recent ruling of TC nº 74/2022 of June 14 , which reproduces them and confirms their validity)

Judgment of the European Court of Human Rights of January 12, 2021 : The Court does not find it unreasonable for the State to consider it necessary to protect its general economic interest in collecting public revenues through public scrutiny aimed at discouraging non-compliance with tax obligations. It considers that this purpose justifies the interference in the rights to privacy and data protection of debtors, even with the publication of their addresses. And it expressly says: " In the circumstances of the case, having made public the information in question could not be considered a serious interference in the personal sphere of the plaintiff. It is not apparent that the publication of his personal data would place a greater burden on his personal life than was necessary to satisfy the legitimate interest of the State ."

It must also be emphasized that the only and legitimate purpose of the duty to contribute is the support of public expenses, that is, the provision of sufficient means to cover the general needs that a social and democratic State like ours must address in its entirety. objective of achieving a more egalitarian and just social order. This connection of the duty to contribute with its social purpose is what turns the individual duty to contribute of each citizen into a matter of general interest that can, in certain circumstances, make said duty prevail over the individual rights of taxpayers.

In other words, this general interest characteristic of the duty to contribute is the one that seeks to obtain sufficient resources to make effective the statement of art. 9.2 of the Constitution: " It is up to the public powers to promote the conditions so that the freedom and equality of the individual and the groups in which they belong are real and effective; remove obstacles that prevent or hinder its fullness and facilitate the participation of all citizens in political, economic, cultural and social life" .

And this real equality and social justice, which are essential to make citizens' rights effective, in turn become, in a kind of perfect legal circle, the essential and guiding principles of both the distribution of the tax burden (system fair tax) and the destination of the income obtained through taxes (equitable allocation of public spending).