The rise of sexual freedom was not unique to England, but part of the general European Enlightenment. Because it has been so little studied, it is difficult to know to what extent its ideals had spread in other countries by the end of the eighteenth century, though it seems clear that they were advancing everywhere. It also seems likely that the pre­cise ways in which sexual liberty was justified differed according to national context.1 All the same, it is obvious that, as had been the case since the middle ages, English theological and philosophical ideas evolved in parallel with those on the continent, and were deeply influ­enced by foreign authors and examples.2 The most extreme exponents of sexual freedom, from Adriaan Beverland to Charles Fourier, tended to come from abroad; whilst all the most influential domestic theo­rists of personal liberty, from Hobbes to Bentham, took their cue partly from international debates on toleration, natural law, criminal justice, and personal ethics.

It is equally clear that the advance of sexual freedom was largely a jumbled, unconscious process. It was not part of any philosophical or political programme: very few thinkers pursued it systematically. It mainly came about through the gradual diffusion of new ways of thinking, and their popular adoption, manipulation and extension. Ideas of sexual liberty could be derived from biblical as well as from militantly anti-religious foundations – just as it proved perfectly pos­sible to use new, radically secular philosophies to uphold conventional morality. In practice, there was no necessary connection between any particular approach and any particular conclusion.3

The transformation of sexual attitudes by 1800 thus came about in a remarkably messy and inadvertent way, from the piecemeal and sometimes incoherent assimilation of old and new points of view. Yet is that not how most ideas spread, and how most of us in practice make sense of the world around us? It was this combination of intel­lectual multiplicity and more general, fundamental shifts in ways of thinking that explains why the development of sexual liberty, though never a central aim of the Enlightenment, was nonetheless one of its most pervasive effects.

It also helps to explain why, as many eighteenth-century thinkers recognized, the ultimate outcome was not a new consensus about the scope of sexual freedom, but rather a greater plurality of moral views, with irresolvable tensions between them. This was not only because of the continued appeal of the orthodox ways of thinking that had underpinned the culture of sexual discipline. It was also inherent in enlightened attitudes towards reason, nature, and society, which, in shifting the parameters of debate, had themselves raised many new questions of principle and interpretation. As the philosopher Francis Hutcheson wrote in 1725, it was easy to see why there was such a ‘vast diversity of moral principles’ in the world – they derived from ‘different opinions of happiness, or natural good, and of the most effectual means to advance it’, from disagreements over ‘public good, and the means to promote it’, and from varying ‘opinions of the will or laws of the Deity’.4

In short, sexual liberty was not a string of agreed conclusions but a set of ideas amenable to many different interpretations. Where pre­cisely was the line to be drawn between public and private acts? What were the limits of ‘natural’ behaviour? How should ‘harm’ be defined, or ‘consent’? What role remained for the state in sanctioning relation­ships, upholding morality, preserving health, defining unacceptable behaviour, and protecting the vulnerable? And what should happen when sexual freedom conflicted with other fundamental values? Compared with the definition of a valid marriage, which had been the central issue in traditional sexual ethics, these were, and still are, much more complicated and intractable questions. As a culture, our answers keep changing; and we can never entirely agree. Often, in fact, we disagree very much: in law, philosophy, politics, and public life, these issues have provoked some of the most contentious debates of the nineteenth, twentieth, and twenty-first centuries.5 But that is the price we pay for trying to base our moral values on reason, rather than on divine commandments.