The concept of rights first became unmistakably prominent during the period of modern intellectual history known as the Enlightenment, which for our purposes had its beginnings in the early seventeenth century and ran to the end of the eighteenth. It was a period in which both the Church and the ancient Greek authorities (who had been rediscovered during the Renaissance) began to be questioned, and the order of the natural world began to be seen as capable of being understood by means very different from those that Renaissance scholars and church scholastics had hitherto been accustomed to using. Francis Bacon’s turning away from scholastic to experimental methods of investigating the world marks the beginning of this period, and we can think of it as ending with (if not culminating in) two political revolutions: the American and the French, which defined the first expansionary period. What began as a new, antidogmatic and inquisitive approach to the study of nature was applied to human affairs, and with consequences that are still unfolding.

A subjective concept of rights – subjective in focusing in an important but as yet unspecified way upon the right-holder – had already emerged at least as early as the late Middle Ages, in disputes among Catholic clerics. It would be a mistake to regard this emergence as an unambiguous mark of moral progress, however. One of the more curious and least reputable chapters in the history of rights concerns the role of the concept of rights in the defense of human slavery. Rights in the sense we have called subjective had had a key role in the Dominican answer to Franciscan communism. That which we use we acquire a right to exclude others from using, and if we wish, we may transfer our right of exclusive use to another in gift or exchange. But implicit in the Dominican answer is the further question: If using things naturally gives the user property in them, does a person not then acquire property in his own body? And if a person has property in himself, why may he not give or trade it away, or put it at hazard? In other words, if people can naturally acquire property in what they use – which they may then trade or risk – why can they not naturally enslave themselves, by trading away or staking their persons and their liberty?