The themes of study centered on man and his practical problems (morality, economics, jurisprudence, etc.), but almost equally on a particular body of work accepted by all of them, as the ground against which to test their disagreements, including at times bitter polemics within the School. Sovereignty The School of Salamanca distinguished two realms of power, the natural or civil realm and the realm of the supernatural, which were often conflated in the Middle Ages through granting royal control of investiture of bishops, or the temporal powers of the pope. One direct consequence of the separation of realms of power is that the king or emperor does not legitimately have jurisdiction over souls, nor does the pope have legitimate temporal power. This included the idea that there are limits on the legitimate powers of government. Thus, according to Luis de Molina a nation is analogous to the mercantile corporations of his time, in that those who govern are holders of power (effectively sovereigns) but a collective power, to which they are subject, derives from them jointly. Nonetheless, in de Molina's view, the power of society over the individual is greater than that of a mercantile corporation over its members, because the power of the government of a nation emanates from God's divine power (as against merely from the power of individuals sovereign over themselves in their business dealings). At this time, the monarchy of England was extending the theory of the divine right of kings—under which the monarch is the unique legatee of God's power—asserting that subjects must follow the monarch's orders, in order not to contravene God's design. Counter to this, several adherents of the School sustained that the people are the vehicle of divine sovereignty, which they, in turn, pass to a prince under various conditions. In this, the late scholastics were instrumental in the development of early modern theories of political representation. Possibly the one who went furthest in this direction was Francisco Suárez, whose work Defensio Fidei Catholicae adversus Anglicanae sectae errores (The Defense of the Catholic Faith against the errors of the Anglican sect 1613) was the strongest contemporary defense of popular sovereignty. Men are born free by their nature and not as slaves of another man, and can disobey even to the point of deposing an unjust government. As with de Molina, he affirms that political power does not reside in any individual, but