the person who gives it. Chapter 18, "The Boycott", discusses the legitimacy of boycotts in a free society. A boycott is an attempt to persuade people to not have any association with a particular person or firm, either socially or commercially. From a libertarian perspective, boycotts are legal and licit because they are purely voluntary and an exercise of free speech and property rights. It is within the rights of those who disagree with a boycott to organize a counter-boycott or to boycott the boycotters. Secondary boycotts, where labor unions attempt to persuade consumers not to buy from firms that deal with non-union firms, are also legitimate, despite their outlawry under current labor laws. The use of picketing as a form of advertising a boycott is a more complex issue because it involves the use of government streets. In a free society, employer devices such as the blacklist and yellow-dog contract would be legal. Chapter 19, "Property Rights and the Theory of Contracts", argues that the right to make contracts derives from the right of private property. Therefore, only enforceable contracts should be those where the failure of one party to abide by the contract implies the theft of property from the other party. The proper libertarian theory of enforceable contracts, according to Rothbard, is what he calls the "title-transfer" theory of contracts. Rothbard argues that mere promises are not a transfer of property title, and the failure to fulfill a contract is an implicit theft of property. He also argues against the prevalent “promise” or “expectations” theory of contracts, which holds that all promises must be enforceable contracts. Rothbard contends that there can be no property in someone's promises or expectations and therefore should not be enforceable. Rothbard argues that a person cannot alienate their will or control over their own mind and body, and these things are inalienable. Rothbard argues that prohibiting someone from working for another employer for a certain period is one step removed from direct compulsory slavery and should be impermissible in a libertarian society. However, employers can voluntarily agree to blacklist the worker and refuse to employ him. Rothbard also explains that if an individual receives payment or a loan based on their future service, and they decide to quit, they must return the payment or loan amount plus interest, as the title to the money was transferred conditionally on their performance. Rothbard also