One of the curious features of the present time is that, even though we are all liberal, there is no agreement about what liberalism means. Some people will tell you that the core liberal value is personal liberty, but others insist it is equality. Some say that liberal values require multiculturalism, while others believe they demand a common culture based on personal autonomy. For some, liberalism is a strictly political theory that applies only to the structure of the state. For others, it is a whole way of life.
These are not just minor differences. They extend to the basic concepts of liberalism itself and to the underlying philosophical beliefs in line with which they are interpreted. If some liberals see freedom as mere absence of interference, others view it as a positive ability to act. For some liberal thinkers, justice requires protecting private property; for others, it means redistribution. Underlying these differences are even larger divergences: some liberals are ardent supporters of rights, while others are defenders of utilitarianism; some are devotees of social contract theory, and yet others are partisans of value pluralism.
What all liberals have in common is a touching certainty that they are right. Liberalism is a missionary faith, and proselytising zeal is not normally conducive to sceptical inquiry. Whatever the core values of liberalism, they can surely conflict with one another - and with other goods such as social cohesion. Yet it rarely occurs to liberals to ask themselves whether their values - however vaguely or inconsistently defined - are viable in the long term.
It is this last question that preoccupies Mark Garnett. In The Snake That Swallowed Its Tail, he argues that a highly individualistic type of liberalism - "the philosophy of the short term, of the speed-dating, cold-calling society" - has come to pervade political life in Britain. In the past, thinkers such as John Stuart Mill had a vision of liberal values in which altruism was prized. As Garnett sees it, Mill's "fleshed-out" liberalism was displaced in the Thatcher era by a "hollowed-out", Hobbesian philosophy in which self-interest is at the centre. Liberalism of this latter kind is ultimately self-undermining, he believes: it can end only by "swallowing its tail", at which point a reaction in favour of saner values will set in.
Few academic writers know enough about the business of politics to be able to write intelligently about the tangled links between theory and practice. Garnett is one of the few, and his arresting and often amusing account of the political history of postwar Britain as a transition from fleshed-out to hollowed-out liberalism will be read with profit by anyone interested in the role of ideas in politics.
This does not mean that his account is always convincing. Like many critics of the narrow version of liberal individualism that has shaped politics since the 1980s, Garnett portrays it as a deeply pessimistic philosophy that owes a great deal to Hobbes. To my mind, it is precisely the opposite. In so far as Margaret Thatcher and her disciples had anything resembling a coherent political vision, it was of a neoliberal utopia.
Thatcher believed that the British economy could be revolutionised, and that at the same time Britain's culture could remain unchanged - or revert to the norms of the 1950s. She never understood that the ideology of choice and innovation she promoted in the economy would inevitably spill over into other areas of life. She believed that unfettered choice would somehow be virtuous, and completely failed to foresee the anomic, crime-ridden society that has actually developed. Like other neoliberals, she seems to have imagined that freedom is the natural human condition - a view Thomas Hobbes scorned heartily, and rightly so.
If The Snake That Swallowed Its Tail has a positive message, it is "Back to Mill" - the embodiment of the fleshed-out liberal philosophy that has supposedly been abandoned over the past generation. No doubt Garnett is right in thinking that Mill's was a superior form of liberalism, but it is hard to see how it can be revived today. He tells us that it will return only "once Britain has been entirely hollowed out". However, to adapt a well-known adage of Adam Smith's, there is much hollowness in a nation - and in liberalism. Most likely Britain will drift on much as it does at present, a country where everyone believes in liberal values, yet no one knows what they are.
John Gray's latest book is Heresies: against progress and other illusions (Granta)