Libertarianism says that people should not cause conflict. It wants everyone to get along. That’s why the non-aggression principle, which libertarianism is based on, is so simple. It does not tell you how to live your life. It just says not to cause problems in the lives of other people. This rule is great in theory, but not in practice. Not because libertarianism isn’t practical. It is. However, applying the non-aggression principle to everyday situations can be quite difficult.
The reason is that people do many different things each day. They make choices and take chances that can potentially affect the lives of other people. Trying to evaluate whether any particular thing you might do will cause conflict, and thus violate the NAP, could take a long time. Try doing that for everything you might do in a day and you won’t have time to do anything else.
So how do we protect liberty without bringing life to halt? What we need is a system that allows us to avoid causing conflict without really thinking about it. Something easy to understand, that gives us 99% of the benefit of the NAP with only 1% of the brainpower. Fortunately, that system already exists. It is called the private property system.
The idea behind property is to refocus our attention from what people are doing, to the physical things that they interact with. Certain things get assigned to people who own them, meaning that they mostly get to decide how they are used. So instead of trying to figure out if chopping down a tree would cause conflict with any person in the world, you would instead ask who owns the tree and how they feel about you chopping it down.
This system makes it really easy to avoid conflict. If you want to do something that involves physical stuff, you simply need to use that stuff according to the owner’s preferences. You should only drive your friend’s car if you have his permission. Following this property rule is very simple. If someone else owns something, get their permission before using it. If you own it, do as you please.
We now have a simple system that works in most cases, but there is still the question of who owns what. So there is another rule that gets us reasonably close to what we would have if we used the NAP. This is called the homesteading principle. Essentially, the first person to start using something becomes the owner. Owners can transfer ownership to others. Also, if someone stops using something, then someone else can start using it. These rules can all be justified by showing that a more rigorous analysis using the NAP will usually lead to the same conclusions.
This is not all there is to it, but we have the basic building blocks of the private property system. This system itself can get fairly complicated, especially when dealing with complex situations involving many people or elaborate types of property, like financial derivatives. Still, it will usually be easier to find a solution to a problem using property rather than looking at a problem on the more fundamental level of the NAP.
That said, some problems simply cannot be solved using the property system. As an approximation, property necessarily only covers a fraction of the possible problems that can arise. There will always be problems that are unsolvable using property. For these problems, one would need to revert back to using the more laborious, but more exact, non-aggression principle.
However, once a more difficult problem is solved a few times, we can build additional measures for sorting out harder problems. Formalized rules for resolving specialized conflicts, templates for solving specific conflicts, case studies on how conflicts were previously resolved, and a whole body of theory has already been developed in different legal systems. To a large extent, these systems already embody the non-aggression principle. This is great because creating a libertarian society would not require much to change from a legal perspective, we could just use all of the good parts of what has already been built.
A frequent point of confusion is when people consider the property system to be more fundamental than the NAP. Private property implies the NAP, but this does not mean that the NAP is derived from private property. On the contrary, it means exactly the opposite. If you uphold the non-aggression principle, then you will find that private property leads to the same conclusions most of the time, but when they conflict it is the property system that is wrong.
People have also tried to justify the property system directly, to get it to stand on its own merit. It is possible to create utilitarian arguments in favor of property, but these apply even more strongly to the NAP. Also, because property is simply an abstraction, it is impossible to devise an impervious theoretical foundation for it on its own. Instead, the libertarian ethical system upon which it is based should be used to supply any justification. Whether you believe that libertarianism is justified is another question, but at least it is a question about a well-formulated system, rather than the rule-of-thumb property system that approximates it.
So for libertarians, the property system is a great boon. It helps to spread the benefits of libertarianism without requiring everyone to read For a New Liberty. Unfortunately, it also leads to some confusion as people lose sight of the ethical system upon which it is based.