 The same good can be excludable at one time, but non-excludable at another, or excludable in one society, but non-excludable in another. For example, radio broadcasts used to be a public good because it was not (easily) possible to prevent individuals from tuning in, but this is no longer the case in the digital age. But technology is only part of the story. A particular plot of land—a prime example of a private good—can be protected by building a fence around it. But there is no fence that cannot be overcome. In reality, a fence is more like a signal indicating that the owner prefers to keep others out, or it makes it more costly for them to do so. What matters for the characterisation of land as a private good is that the landowner has the right to stop potential trespassers and that this right will be enforced by the legal system. Of course, which sets of rights are attached to property depends on the norms prevailing in a society. Property rights are never absolute (property in a chain saw gives me the right to use it to cut my own trees but not to cut my neighbour’s trees, much less to use it to hurt anyone), and always the result of past negotiations.