It has become distinctly unfashionable to suggest the tax system should be used to redistribute wealth. The latest Labour politician to put the case that the aspirations of a growing middle class preclude tax increases to pay for welfare benefits is David Blunkett, Labour's education spokesman.
He told an audience in Birmingham last week that the voters in 1992 rejected the notion that government could claw back cash in order to fund pension and child benefit changes which they could not see as being directly beneficial to themselves and their family.
The Liberal Democrats will be the only party going into the election promising higher taxes, and they are intent on stressing the increases will amount to only 45p a week for the average taxpayer.
The promise is that an extra #163;10 billion would be spent by the Liberal Democrats over five years of government. The same commitment was given before the last election, but Mr Foster has produced detailed breakdowns for the money's destination.
Around half would pay for smaller classes in primary schools, high quality pre-school education, and new books and equipment for schools. According to Mr Foster, the costings on smaller classes are more realistic than those of Labour. The Liberal Democrats estimate it would cost around #163;1.2 billion over five years to reduce all primary classes down to 30 or fewer. Mr Foster does not believe Labour could deliver its commitment to smaller classes for five to seven-year-olds by re-directing money from the assisted places scheme.
The Liberal Democrats envisage spending rising from around #163;90 million in the first year to #163;420 million after four years. The figures take account of the cost of training the extra teachers, but not the cost of buildings.
Similar sums will be needed to pay for expansion of pre-school education. Mr Foster would simply scrap nursery vouchers and require local authorities to ensure there are places for all three and four-year-olds whose parents want them to have nursery education.
Spending would rise from #163;99 million in the first year to #163;488 million in the fifth - the figures assume that all four-year-olds would take up a place, and 80 per cent of three-year-olds.
There is the same precision in the five-year spending plan for books and equipment. The Liberal Democrats would double spending to #163;626 million in the first year and the sums would reduce down to #163;135 million by the end of a term of government.
A substantial share of the #163;10 billion would be required to fund the Liberal Democrats' ambitious plans for training; additional support for further education and to provide for higher education. Those figures are to be produced in the next few weeks.
This time round, Mr Foster is producing detailed costings because he has tired of the accusation that the Liberal Democrats have an elastic approach to what their #163;10 billion might buy - that creative accounting allows them to spend the money many times over.
It is perhaps more a mark of how far Labour has shifted its policies that there is such a gap between the two centre-left parties. As well as increasing tax levels to pay for improvements in education, the Liberal Democrats would return grant-maintained schools to local education authorities and scrap exam league tables.
There is much in Mr Foster's approach that meets approval from a beleaguered teaching force. He wants to see a slimmed down national curriculum and he wants politicians to stop telling teachers how to teach.
More fundamentally, he insists it is dishonest of politicians to will the ends - higher achievement in schools - without producing the means. He cites the findings of the Office for Standards in Education on the adverse effects of book and equipment shortages in schools.
However, Mr Foster admits to being uncertain about whether Labour is correct in its assumption that the aspiring classes are no longer willing to forfeit part of their income to fund improvements in services from which they gain no direct benefit.
He says: "Payment of income tax is a subscription to a civilised society. It is only fair that payment for services should be required in relation to ability to pay."
Critics maintain that spending promises are easy for the Liberal Democrats to make because they will not win enough seats to form the next government.