Once every 20 years or so, a set of ideas coalesces which fundamentally change the politics and future of the country.
It happened with planning in the late Fifties and early Sixties - the idea that led to the neo-corporatism of the now defunct National Economic Development Organisation, to beer and sandwiches at Number 10, the great Robbins expansion of the universities, and the massive reorganisations of central and local government and the NHS that characterised the Sixties and early Seventies.
It happened with monetarism in the mid-Seventies - Keith Joseph's decisive break with Keynesian economics on whose coat-tails Thatcherism was launched.
It happened most famously with the Beveridge report of 1942, which led to the founding of the modern welfare state.
It may be happening now with the publication of a series of recent studies on the welfare state of which yesterday's Dahrendorf report on Wealth Creation and Social Cohesion is the latest.
What marks these moments is not that one party adopts the ideas, but that they come to infect all parties. They do not lead to instant consensus, in the sense that there is a new and sudden unanimity about what should be done. When they happen, the party battle around them remains fierce. But the ground on which the battle is fought suddenly shifts. And as a result the world changes.
Thus with Beveridge. Although the wartime coalition adopted Beveridge's report with its clarion calls for full employment, a national health service and a new "cradle to grave" social security system, a fierce Whitehall battle against the proposals was fought, with Sir Kingsley Wood, the Chancellor, damning the package as "an impracticable financial commitment".
Although the coalition set in train the work that became the NHS, free secondary education for all, social security, and Keynesian economics, it took the Conservatives until the late Forties to fully accept the new dispensation.
The same was true of monetarist economics. The ideas infected Labour while it was still in government. The first Prime Minister to warn that "the cosy world we were told would go on for ever, where full employment would be guaranteed by a stroke of the Chancellor's pen - cutting taxes, deficit spending - that cosy world has gone" was not Margaret Thatcher. It was Jim Callaghan in 1976. After 1979, it is true his party swung left again, fighting Mrs Thatcher tooth and nail until she fell. But that changed economic vision, though attenuated, now profoundly influences the policy of Blair and Brown.
Yesterday's Dahrendorf report may mark the culmination of a similar shift. For it is almost the last of a string of free enterprise reports strung out over the past three years which have attempted to forge a new settlement for the post-Thatcher age - one which takes the best of the tools that the Iron Lady used but rejects much, if not most, of her philosophy.
These reports have been remarkable for not being the work of government. They have been the product of the great and the good. They have been funded by fiercely independent charitable money and, where commissioned by Labour and the Liberal Democrats, have been commissioned at arm's-length to allow the parties to distance themselves from the conclusions. And - an important point in the forging of an agreement about the issues to be addressed - they have been supported not just by those never reconciled to the Thatcher project but by people who gained from the Thatcher years and who worked during them as civil servants and government advisers.
The first, in November 1992, was the National Commission on Education. Originated by Sir Claus Moser, the former Chief Statistician, and funded by Paul Hamlyn, the publishing millionaire, it demanded a massive reinvestment in education.
Then came the Carnegie Inquiry into the "third age" - those coming up to and just past retirement. …