There are numerous conceptions of where law, rights and property come from. They all hinge on various assumptions dealing with the question of human nature.
"Natural law" and "polycentric law" is like a naturalization process whereby rules form spontaneously over time, not necessarily from deliberate human design, but as a consequence of human action that did not even necessarily intend to create such a law. It is law that is not necessarily tracable to a single origin. It arises out of society's need for social cooperation. It is the law of social cooperation. Polycentric law arises out of voluntary agreement by all individuals and parties involved. Understood in an evoluntionary sense, it arises out of man's need to adapt to their environment and fullfil what's necessary for the general well-being of the species. Natural laws can also be seen as archetypes, as universalities that make their way into all cultures in one form or another.
Some people deny that there is such thing as any natural law, or that there are no natural laws of human action. This claim requires one to reject the natural sciences entirely if it is to be taken seriously. Is the natural sciences not the source of the discovery of the laws of nature, of the physical universe? The universe is not completely subjective and arbitrary. The universe functions on the basis of specific natural laws. Humans are part of the universe. Humans, too, function on the basis of specific natural laws, in accordance with those of the physical world. Humans, like all other physical objects, have a specific nature.
In the physical sense, the field of biology sheds some light on human nature. The field of economics, or more specifically praxeology, has also uncovered laws of economics that are essentially laws of human action. Psychology, while it has been boggled down in absurdity by some, has also yielded a certain level of insight into human nature. And our general experience as human beings gives us some insight into our nature, and has lead to what could be called a certain "moral sense" as to our individuality as well as to our relationship to other individuals. As Herbert Spencer once observed, people support the rights of others in proportion to their sense of their own rights.
One view of human nature that manifests itself historically in all sorts of ways is the Hobbesian state of nature concept. The Hobbesian claim that in the abscence of a central authority everyone is at war with eachother is an unfounded dogma that leads to radical pessemism, and of course, a reliance on central authority. Locke, on the other hand, while he was certainly flawed, had a much better conception of human nature than Hobbes did, because Locke actually recognized the existance of the sovereignty of the individual.
The Hobbesian concept of human nature has served power well historically. It inherently must lead to an assumed necessitity for central state authority, lest there be chaos. It manifests itself in modern politics in all sorts of ways. To many modern leftists, for example, if social programs were cut or if welfare were privatized there would be a drastic increase in poverty. To many modern rightists, for example, if we pulled out of Iraq or if we ended the drug war, people would be dieing left and right from overdoses and our country would be turned into a theocracy imposed by Muslims by invasion. The hobbesian concept uses fear to obtain obedience to central authority.
Herbert Spencer put forth a naturalist view where the Hobbesian "war of all against all" was the conditions necessitated in man's earlier state, and that man's state has advanced to a degree since then through social evolution. The degree of tyranny that exists today is the inertia left over from the earlier conditions of man's living where brute force was "necessary" for survival. On the other hand, on an individual basis more and more people have decided to live largely voluntarily as time has passed; social conventions changed as to outlaw barbarisms of the past such as burning people at the stake in public and the popular use of torture.
Man has not yet fully adapted to the voluntary state. That does not mean that he is incapable of adaptation, and has not made some progress towards adapting towards the voluntary state already. In the west, we have suceeded in rolling back the church-state and chattel slavery. In the 18th and 19th century, fuedalism and monarchy were rolled back meaningfully for the first time in the west. This does not mean that vestiges of them do not still exist in our society, of course. But the social progress also has its own inertia. It has manifested itself in modern times in technological and economic progress, as well as some minor improvements in social interrelations.
On the other hand, social retrogressions are possible. We have been going through one ever since the 2nd half of the 19th century, with the rise of the warfare and welfare state around the world. While social progress has gone on somewhat in social interrelations, technology and capital formation, the rise of the modern democratic state stands as a bulwark of coercion pushing back in the other direction.
The degree of slavery and war, and tyranny in general, in history has been directly in proportion to the degree to which coercive government exists. In short, coercive government was "necessary" to a more primitive state of man than the current one. As history progresses, as technology improves, as cooperation and voluntary methods prove to be obviously more efficient, as capital forms, government becomes less and less "necessary". It is nonsensical to presume that government is a necessarily permanent institution.
Unfortunately, there is a disease. It's called legal positivism. The legal positivist defines rights as whatever the government recognizes to be rights in the positive law at the given moment, which can only fall back on the status quo. The legal positivist believes that all law, all rights and property itself derives from government. This is a false definition of law and rights. It simply assumes that all rights are just privileges given to us by a government, that rights come from governments. This is a profoundly anti-liberty notion in its implications.
The adherants of natural law cannot disagree more strongly with the positivist. To use a classic phrase, "liberty is the mother, not the daughter, of order". Rights precede governments. Laws precede governments. Civilization precedes government. Property precedes government. Government did not invent property. Government did not invent liberty. Governments do not legislate rights into existance. At best, all a government can do is recognize a pre-existing right. To presume that it's all the literal creation of government yields to the notion of omnipotence, it merely regaurds the government as a god.
The positivist is wrong in assuming that there is no such thing as non-governmental law. Not only is there a long history of privately produced law, but we live in a world in which there already are plenty of forms of non-governmental law all around us. The positivist assumes, without any logical explaination as to why, that the only type of law is monocentric law. They ignore the existance of polycentric law at their own peril. At best, all they can do is fall back on some kind of hobbesianism to try to justify the status quo. On the other hand, only a natural law and natural rights position can genuinely hold the status quo up to an independant yardstick.
It is precisely the positivist conception of law and rights that has allowed tyranny to be excused in this world. It is precisely the positive line of reasoning that tyrants use to justify their actions. And it is precisely the positivist conception of rights that allows those same alleged "grantors" of rights to remove their protection. Positivism can only provide blind sanction to whatever the state does when taken to its consistant conclusion. The positivist must rationalize the irrational with the saying, "its the law, so it must be followed". This rules out any notion of civil disobedience and justice vs. injustice.
It should be quite obvious as to why rights, liberty, property and law precedes government. People freely acting is something that happens anyways, regaurdless of wether or not there is a government. Even the most totalitarian government is not capable of enforcing the total illegalization of liberty. Even the strongest prohibition cannot eliminate a good or services use entirely. Property is something that naturally arose out of homesteading and voluntary exchange; and the formation of a government requires pre-existing property, particularly the property of those funding it, those providing the property necessary to its creation and maintenance. And law is simply the enterprise of subjecting human conduct to the governance of rules. Law could be something as simple as a household rule, or a complex network of private contracting.
If law and rights are defined as whatever those in the government arbitrarily decide they are, which is essentially what legal positivism does, then one cannot claim to have any rational basis for asserting any rights at all and therefore may as well be entirely complacent to the existing regime. Since everything is allegedly entirely subjective and arbitrary, then this whole political science and economics thing is a gigantic waste of time, and everyone should just stop trying to learn about and solve social and economic problems. On the other hand, if there is an actual basis for law and rights that can be derived through reason from objective facts about human nature, then we should continue the process of learning exactly what that is and what it entails.
One finds endless examples of how the presumption that there is no law other than positive state law is false. Private law and customary law existed in various forms in pre-state societies. Even in the most primitive of societies, there were rules that were derived so that the people could conduct their affairs in a more conductive or productive manner. One finds that much of what is considered the "common law" in the west originally derived from pre-existing private law, such as the law merchant of the middle ages. There is no reason to believe that it is impossible for a private contract or voluntarily agreed upon rule to constitute a law.
The critics of natural law tend to denigrate human reason, while mysteriously not applying this denigration to those who make up the government. Afterall, if the idea is that man is so evil and flawed that he cannot be trusted, then why shouldn't this apply to the government? Some assert that natural law is just a cover for religion, that it is inherently a religious concept meant to impose social conventions onto others. But this is an ignorant interpretation of natural law. It has been understood in an entirely secular context for a long time. Some critics essentially espouse the doctrine of moral relativism. But if everything is as relative as they make it out to be, then there can be no such thing as law or rights at all.
What is so crazy about the idea that ethics, rights and law can be formed objectively on the basis of human reason? What is so crazy about the idea that law can and does exist and form in a non-governmental context? What is so crazy about the idea that there can be a scientific ethics? What is so crazy about the idea that law and rights should be judged on the basis of logic just like anything else? The alternative is nothing but ad hoc authoritarianism.