other essential conditions of law be observed..." Human law is positive law: the natural law applied by governments to societies. Natural and human law is not adequate alone. The need for human behavior to be directed made it necessary to have Divine law. Divine law is the specially revealed law in the scriptures. Thomas quotes, "The Apostle says (Hebrews 7.12): The priesthood being translated, it is necessary that a translation also be made of the law. But the priesthood is twofold, as stated in the same passage, viz, the levitical priesthood, and the priesthood of Christ. Therefore the Divine law is twofold, namely, the Old Law and the New Law." Thomas also greatly influenced Catholic understandings of mortal and venial sins. Thomas Aquinas refers to animals as dumb and that the natural order has declared animals for man's use. Thomas denied that human beings have any duty of charity to animals because they are not persons. Otherwise, it would be unlawful to kill them for food. But humans should still be charitable to them, for "cruel habits might carry over into our treatment of human beings." Thomas contributed to economic thought as an aspect of ethics and justice. He dealt with the concept of a just price, normally its market price or a regulated price sufficient to cover seller costs of production. He argued it was immoral for sellers to raise their prices simply because buyers were in pressing need for a product. Political order Thomas's theory of political order became highly influential. He sees man as a social being that lives in a community and interacts with its other members. That leads, among other things, to the division of labour. Thomas made a distinction between a good man and a good citizen, which was important to the development of libertarian theory. That indicates, in the eyes of atheist libertarian writer George H. Smith, that the sphere of individual autonomy was one which the state could not interfere with. Thomas thought that monarchy is the best form of government, because a monarch does not have to form compromises with other persons. Aquinas, however, held that monarchy in only a very specific sense was the best form of government––only when the king was virtuous is it the best form; otherwise if the monarch is vicious it is the worst kind (see De Regno I, Ch. 2). Moreover, according to Thomas, oligarchy