tribal aristocracies to avoid class war. The ruling class in Plato's best state has an unchallengeable superiority and education. Breeding and training of the ruling class was necessary for ensuring stability, and Plato demanded the same principles be applied as in breeding dogs, horses, or birds. Popper summarizes Plato's systematic historicist sociology, which was an attempt to understand and interpret the changing social world. Chapter 5, "Nature and Convention", introduces Popper's distinction between natural laws and normative laws. Popper divides stages of the development of this distinction throughout history, and then applies it to a further analysis of Plato. According to Popper, natural laws describe strict, unvarying regularities in nature, such as the laws of motion and gravity, while normative laws are rules that forbid or demand certain modes of conduct, such as the Ten Commandments. Normative laws can be enforced by people and are alterable, whereas natural laws are beyond human control and unalterable. Popper believes that this distinction developed throughout history, starting from a naïve or magical monism, where there is no distinction made between natural and normative laws, and unpleasant experiences are the means by which people learn to adjust to their environment. Within this stage, there are two possibilities: naïve naturalism and naïve conventionalism. In the latter possibility, both natural and normative regularities are experienced as expressions of and dependent upon the decisions of man-like gods or demons. The breakdown of magical tribalism is connected to the realization that taboos are different in various tribes, that they are imposed and enforced by man, and that they may be broken without unpleasant repercussions if one can only escape the sanctions imposed by one's fellow-men. The development ends at what Popper calls critical dualism, which is the idea that norms and normative laws can be made and changed by humans, and cannot be derived from natural regularities or laws, although they are not necessarily arbitrary. This position was first reached by the Sophist Protagoras. It emphasizes that humans are morally responsible for norms, and should try to improve them if they are objectionable. It can also be described as a dualism of facts and decisions, meaning that decisions must be compatible with natural laws to be carried out, but they cannot be derived from those laws. Decisions can refer to a certain decision that has been made or the act of deciding itself. According to Popper, there are