Will the left focus on what money can't buy, or on what money shouldn't buy?

Alex Hern speaks to Michael Sandel about morality in politics and the markets.

A woman gives blood in Germany. Research has found that paying for blood can lower the amount offered. Photograph: Getty Images

Once acquired, stereotypes can be hard to overturn, and it's hard to think of a more enduring stereotype of the British political divide than a hard-headed Conservative making "difficult decisions" which the left decry as immoral. Those of us on the left, we are told over and over, must fight the stereotype by pushing for policy which is efficient on its own terms, and not just "moral". So the argument against forced unpaid work cannot just ride on the obvious truth that that is an unpalatable policy for 21st (or 18th) century Britain; it must also address whether such work succeeds in getting people jobs.

But, argues Michael Sandel, Bass Professor of Government at Harvard University and author of What Money Can't Buy: the Moral Limits of Markets, the can pendulum swing too far the other way. "I think that left-wing politics is diminished and impoverished when it tries to limit itself to efficiency arguments alone," he tells me when we sequester ourselves inside the New Statesman's offices on a sunny bank holiday Monday. "The result is a managerial, technocratic kind of public discourse that ultimately fails to inspire."

Sandel knows about inspiring people. What Money Can't Buy has made a splash in the British political scene since its publication: After the Guardian said it should be "the bedside companion of every Miliband aide", the Labour leader himself pronounced it "a powerful argument for change", and invited the philosopher to speak at the party conference last autumn.

The strength of its message comes from linking arguments about what money can't buy – the ones the left grudgingly feels it ought to make – with arguments about what money shouldn't buy. One of the book's case-studies is of some Israeli nurseries which introduced cash penalties for late pick-ups; counter-intuitively, the number of tardy parents actually increased as a result. But even if it hadn't, it would still have turned late pick-ups from something parents felt guilty about to something they could treat as a service they bought.

"So there are these two separate, overlapping arguments," Sandel explains. "One is that the the cash incentives may backfire as a practical matter; the other is, even if they don't backfire in terms of producing less of the behaviour being sought, they may crowd out attitudes and norms, non-market values, worth caring about."

Sandel blames this crowding out on the tendency in social sciences, all across the spectrum, to seize on things that can be weighed and measured, to the exclusion of other areas on import. "When economics was invented by Adam Smith, he conceived it, rightly I think, as a branch of moral and political philosophy. In the 20th Century economics and the social sciences tried to establish themselves as autonomous disciplines, as value-neutral sciences, and I think much has been lost as a result."

"One of the ways I've tried to challenge economistic ways of thinking about social life is to show how, even within efficiency terms, ignoring norms ignores something important."

But doesn't bringing morality into the debate risk being seen as a capitulation? After all, we've spent so long fighting political battles on the basis of narrow claims of efficiency that to abandon them now might be seen as an admission of defeat.

"I disagree," Sandel says when I put it to him. "I think one of the reasons that there is such wide-spread frustration with the existing terms of public discourse, and with the alternatives on offer from the major parties, in democracies around the world, is that there's too much focus on managerial and technocratic concerns, and too little vision."

The left has seized on that message, but there's another nut for Sandel to crack before he can claim victory. "Some strands of Conservative political thought want to bring ethical questions to bear on politics. And so I was hoping to connect with that strand as well." Has he? "I think it remains to be seen."