But do they? They have outward signs of existence as a party, such as MPs, thousands of councillors, scores of floppy discs of policy and a meaningless logo. But political parties are ultimately defined by their big purpose. The Conservatives' purpose is to be in power under all conditions. Labour's is to be a broad movement on behalf of the bottom dog. And the Liberal Democrats, pressed into a corner, are . . . what? Well, they are all, unshakeably, in favour of achieving proportional representation, even if they prefer to dignify this as 'pluralism' or 'openness'.
This is, of course, a good thing. But it is too small a thing to constitute a purpose. Worse, the more weight put upon it, the more self-destructive it becomes, since once voting reform is achieved, the party ceases to stand for anything in particular and presumably subsides into irrelevance. If voting reform was all that modern Liberalism was about, then the party would have little chance of avoiding being ingested, over time, by a moderate Labour Party. Lib Dems would be on the road to becoming the student wing of a reformist movement led by the Blair boys - faintly rebellious, noisy, but less and less distinctive, the Independent Labour Party of our days.
And this may happen - it is the secret fear of many activists. But it would be a pity. To see why, let us turn to some senior Liberals. First witness is Sir Russell Johnston, the veteran MP, who told a meeting yesterday: 'Liberalism is not defined by a list of policies. Liberalism is an attitude of mind.' There was a thunder of assent.
Second, Michael Meadowcroft, who refused to join the merged party and leads the breakaway Liberal Party, quoted an old party worker explaining why Liberals kept going during the bleakest years of post-war politics: 'We couldn't stand the Tories and we didn't trust the state.'
That faintly stroppy individualism seems to me the essence of Liberalism. The true Liberal is a troublemaker, out of step on principle, eternally suspicious of all given truths, established authorities and accumulated powers. But because dissent is a lonely business, requiring moral self-sufficiency, Liberals have also tended to be a touch self-righteous. John Buchan, the Scottish Tory novelist, reckoned the difference between his lot and Liberals of a century ago was that the Tories may have considered themselves better born, but the Liberals knew they were born better.
In the end, then, Liberalism is a psychological condition rather than a programme. But it matters to the rest of us because this stroppiness is a politically useful corrective to the deference of voters and the arrogance of rulers. It may be quirky. It may sometimes be annoying. But the Liberal psychology expresses itself politically as an overwhelming bias to liberty. Here is a third witness: 'I remained a socialist for several years . . . and if there could be such a thing as socialism combined with individual liberty, I would be a socialist still. For nothing could be better than living a modest, simple and free life in an egalitarian society. It took some time before I recognised this as no more than a beautiful dream; that freedom is more important than equality . . .'
That was written by the recently deceased philosopher Sir Karl Popper. Politically, Popper tends to be bracketed as a right winger, because of Margaret Thatcher's admiration and his polemical work The Open Society and its Enemies, which attacked Plato, Hegel and Marx. But as the above shows, he was really a liberal, and he is of great relevance to this week's gathering at Brighton.
Popper has the important Liberal characteristics: his Viennese father was a disciple of John Stuart Mill; he was, as a child, 'somewhat puritanical, even priggish'; and he was in revolt against the obtuseness of established authorities. (Ironically, The Open Society failed to find an American publisher in the early Forties because it was too irreverent about Aristotle.) Popper was also highly argumentative, once famously provoking old Wittgenstein to wave a poker at him.
Above all, though, he had a message which the Liberal Democrats need urgently to hear. The Open Society was not simply aimed at the gods of the mid-century horror, but at the very notion of inevitability, or grand historical plans. Well, there are plenty of determinists today. Smug conventional wisdom comes not from the gurus of state power but from other self-satisfied souls, the market economists who believe millions of people to be simply surplus to requirements, the health fascists, the worst excesses of political correctness. And the test of Liberal purpose is the extent to which the party is prepared to remain a movement of stroppy moralists. It is the key to their utility.
There is no question but that, after 15 years of Tory power, they are an anti-government force, but they do not therefore need to be swallowed up by Labour. It was ludicrously suggested at the weekend that Tony Blair was considering using the Lib Dems as a force for stability in a future Labour administration, a counterbalance to the Labour left. If they fall for that - a role as bland Blair-supporting middlemen - they've had it. There are too many complacent councillors and dull careerists already, too many people who think proportional representation followed by a ministerial Rover is what Liberalism is all about.
In fact the great service the Lib Dems could offer Britain would be as a force for instability in a Labour-led government - challenging the pressure groups, defending unpopular views and groups, and generally ensuring that a Blair administration didn't subside into self-deluding Westminster hubris. That would be worth doing.
These are not necessarily going to be easy times for liberal values: Labour will be tempted to compromise incessantly to win power, and to keep it.
So long as the key distinction between Labour and Liberal Democracy is not voting reform but the dissenting nature of Liberalism itself, Russell Johnston's 'attitude of mind', this party can do some good at the end of this century, as it did at the start.
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