degenerates more easily into tyranny than monarchy. To prevent a king from becoming a tyrant, his political powers must be curbed. Unless an agreement of all persons involved can be reached, a tyrant must be tolerated, as otherwise the political situation could deteriorate into anarchy, which would be even worse than tyranny. In his political work De Regno, Aquinas subordinated the political power of king to the primate of the divine and human law of God the creator. For example, he affirmed: According to Thomas, monarchs are God's representatives in their territories, but the church, represented by the popes, is above the kings in matters of doctrine and ethics. As a consequence, worldly rulers are obliged to adapt their laws to the Catholic Church's doctrines and determinations. Thomas said slavery was not the natural state of man. He also held that a slave is by nature equal to his master (Summa Theologiae Supplement, Q52, A2, ad 1). He distinguished between 'natural slavery', which is for the benefit of both master and slave, and 'servile slavery', which removes all autonomy from the slave and is, according to Thomas, worse than death. Aquinas' doctrines of the Fair Price, of the right of tyrannicide and of the equality of all the baptized sons of God in the Communion of saints established a limit to the political power to prevent it from degenerating into tyranny. This system had a concern in the Protestant opposition to the Roman Catholic Church and in "disinterested" replies to Thomism carried out by Kant and by Spinoza. Psychology and anthropology Thomas Aquinas maintains that a human is a single material substance. He understands the soul as the form of the body, which makes a human being the composite of the two. Thus, only living, form-matter composites can truly be called human; dead bodies are "human" only analogously. One actually existing substance comes from body and soul. A human is a single material substance, but still should be understood as having an immaterial soul, which continues after bodily death. In his Summa Theologiae Thomas clearly states his position on the nature of the soul; defining it as "the first principle of life". The soul is not corporeal, or a body; it is the act of a body. Because the intellect is incorporeal, it does not use the bodily organs, as "the operation of anything follows the mode of its being."