Property rights include the freedom to engage in contracts, that is, voluntary associations (cf. pp. 4.6:36-7). In order for an association to be truly voluntary, of course, all parties must participate without coercion. Probably the simplest example of such a voluntary association is the exchange of goods (property) between two human beings.

How are other well-known "rights" implemented in a free society, based on the principles of liberalism?

The right to freedom of speech, like other legitimate human rights, can be reduced to property rights: a human being has the right to full use of his or her own voice, together with any microphones, auditoriums, and other means that he or she may own or else borrow or rent in free exchange with others. A speaker does not, of course, own or have automatic access to the ears of others. When freedom of speech is framed in terms of property rights, some perplexing paradoxes are resolved. Consider, for example, the famous query: "Do you have the right to cry 'fire' in a crowded theater?" By entering a theater, we assent to an implied contract with its owner, whereby we will not interfere with the theater's intended function or needlessly disturb or endanger other patrons. This scenario does not entail any abridgement to the principle of rights, as some imagine. On the contrary, any limitation on our behavior in the theater stems from the need to respect the property rights of the theater owner and other customers and to apply those rights consistently.