This paper addresses the relationship between theology, debt, taxes and evasion between the fourteenth and sixteenth centuries, above all by comparing the idea of "servitus" to that of citizenship. In the world of Italian and European communes, theological reflection faced the question of the legitimacy of gains derived from forced loans to subsidize the public debt. In the monarchical context, the scholastic tradition gradually legitimized the regular and direct tax levy by the sovereign over his subjects. In the early modern period the growth of the tax burden and the public debt pushed some theologians to question the legitimacy of the charges and to cast doubt on claims that tax laws were binding on the consciences of the faithful, as the moral lexicon linked to the city or to the idea of a contract between the monarchy and the body social was fading. In Spain, theological discussion concerning taxes had a unique character because the bull of "Cruzada" granted to the sovereigns the alms paid by the faithful to fulfill the precept of restitution of the "turpia lucra", including evaded taxes.