Natural Law Theory
The Theory of Natural Law states that the needs, behaviors and rights of all humans are based on the rules of nature. One of the most well known supporters of this theory was St. Thomas Aquinas, who wrote the "Treatise on Law" which claimed that human morality follows the same rules that are found in nature, and therefore the rules of nature are binding for all of humankind.
Natural Law Doctrines
There are three guiding principles to the theory of natural law. They are designed to show that laws and their meanings originate from nature and not from humans. Believers in these doctrines feel that it is not up to any person to create their own rules or design their own rights, but instead believe that the rules and guidelines that all people must adhere to were created already created by nature.
The first doctrine states that all laws which are truly just and fair are found in nature. These laws may be observed and discovered but they can not be created. Those who adhere to this belief would feel that any rules or statutes specifically created by mankind are not legally binding.
The second doctrine states that the rules of nature must be used as a guideline to resolve all conflicts. It is believed that common law can be a part of this process because common law is not dictated by any executive action, but it is an ever growing and changing set of laws that can be examined and modified by judges and based on the laws of nature.
The third doctrine states that a law can only be understood and defined based on moral principles that are found in nature. These principles can not be created or devised, they must instead be inherent in nature.
The Overlap Theory
This theory suggests that there is a well defined and unconventional relationship between morality and laws. In other words, it indicates that all laws have some basis in natural morality. Thomas Aquinas supported this theory, and stated that humans have an inclination towards being good and moral beings. It is that concept of morality which guides the idea that all laws are based on morality, and that the morality we must follow is found in nature. Supporters of this theory also understand that some basic laws and principles are not bound by moral guidelines, but believe that any law pertaining to behavior and humanity must be based on morality.
While not every believer in Natural Law Theory agrees on every aspect of the concept, they do all agree on the basic guiding principle that all just laws are based on the concepts found in nature and that those rules should be used to govern over humankind.