David Walker talks to Partha Dasgupta (right), the Cambridge economist who has focused on the third world's economic dynamos: women. Squatting; cooking; suckling; spinning; water-carrying; herding; planting; grinding . . . yashmak'd, sari'd, bare-breasted. Images of third world women tend to the passive, the put-upon. They are down-trodden, done-to. They are not, the gender of the noun signifies, economic actors.

The literature on development has passed them by. Markets, investment, savings ratios: the apparatus that economists, Marxist and liberal, have brought to bear on the third world has had a muscular, manly feel to it.

No longer. No one man, however sharp, no one book, however influential, is going to change a habit of mind let alone a conservative academic discipline; but it is a fair assumption that all development economists, and third world studies of all kinds, will have in future to pay attention to the gender subversion in Partha Dasgupta's An Inquiry into Wellbeing and Destitution, which appears in paperback later this month.

For Dasgupta's women are not passive. He uses the female pronoun a lot, not as a gesture of political correctness, but to signify the centrality of female experience in third world "economic" activity. For his is a big, and disturbing claim: you cannot even begin to understand the facts of economic life in the third world without understanding the dynamics of households, the relationships of parents and children and, above all, the nature of women's work.

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They do not just bake, sew, tend and nurture. They buy, sell, borrow, save, invest and repay, and how much more of each could they do if conditions were right - and how much would that affect fertility, and the possibility of material progress. Neither veils nor mullahs nor a multitude of cultural givens about the place of women in the order of things thwarts Dasgupta's argument and conclusion, that third world women, like first world women - and men - are motivated to better the lot of their children and themselves, that they want to feed themselves next year, that they want a better life. "Ask them," he says, "when they are not being terrorised."

He is - unashamedly - a universalist. Human nature has a common structure, in Bihar as in Brabant and Alberta. Sex, affection, regard for kin, ambition for self and offspring, market behaviour, too: these form a natural anthropology. It is a short step to saying - which he does - that freedom to choose and to achieve is the human norm, much of the rest is oppression. To assume anything else is patronising of those women, besides there is empirical evidence - look at the women of Bangladesh who, despite the disapproval of husbands and priests, have been using credit unions and rudimentary savings and loans operations to borrow trifling amounts - for cottage industry, buying a loom, running a tea stand - and repaying them.

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Economics has recently been under assault. How justified are its cornerstone assertions about rationality in human behaviour; of what value are its mathematical models, the formal elegance of which seems to correlate with their inadequacy as a guide to real events, institutions and people?

Dasgupta is not a doubter. He says there is a common language in which the lives of the rural poor in Asia, Africa and Latin America can be discussed. Behaviour, even of the most intimate kind, can be interpreted in a formal manner. Let us anyway assume we can model behaviour, he says, then test the implications against evidence from the third world. For example procreation can be put into a calculus about the contribution children can make to a destitute household. Children are producer goods. Nutrition is about ratios of calories in and energy expended. The point about the equations is that they demonstrate connections: high birth rates may be caused by environmental degradation.

He has no truck with the suggestion - less fashionable now perhaps than it was a decade ago - that different cultures exhibit different rules, and it is an act of intellectual aggression (neo-imperialist indeed) to foist our western rules on them. Ideas and rules for social justice, as expounded by the likes of John Rawls, can apply in the third world; what Dasgupta offers is political philosophy as amended for conditions of destitution, Rawls for Rajasthan, as it were.

This makes him sound like an apostle of liberalism - James Mill and the utilitarians having a second chance at conquering the sub-continent. "Yes, I am a liberal in the sense of seeing that people want to get on with their lives . . . For too long we have identified the state with its citizens."

It is, he emphasises, positive liberty he wants: a freedom to aspire that becomes operational only once government has provided health care and water. This is no recipe for Thatcherite free markets, however much he appreciates the work of earlier development economists such as Peter Bauer who were intensely critical of the role of governments and aid strategies.

An Inquiry into Well-Being and Destitution in the Third World does not blame - capitalism, western banks, governments which contribute tiny fractions of their budgets to aid. Poverty, indeed, in Dasgupta's words is not just "distributive failure" - just looking at the condition of the third world as one of inequality will not get you far. Something is going wrong in the way resources are allocated within the poorest countries, and it lies in the connection between their population growth and the erosion of their natural resources, and that in turn has to do with the malfunctioning of the household economy. Markets that typically function in advanced industrial economies are often absent in rural communities. Households decide, for example to have children, in order to circumvent the limitations imposed upon them by the lack of trading and commercial opportunities.

How well all that sits within the recent Marxisant and Keynesian traditions of the Cambridge University economics faculty is open to question, but Partha Dasgupta is a Cambridge academic to his fingertips. Born in India, he was an undergraduate at Trinity College, switching from mathematical physics to pursue an economics doctorate; he now holds a fellowship at St John's and the chair formerly occupied by Joan Robinson. His study looks out over the crenellated back of Selwyn College.

Yet his intellectual life is global, made up of international conferences, faxes to colleagues in the United States, Malta, New Delhi, a multitude of papers in that refined form of competition - for novelty, for intellectual rigour - that characterises leading lights in all modern disciplines. He eschews consultancy and though he has friends in public life and government, does not comment on India or aid politics. It is a comfortable life, and therefore one at the other end of the pole from the woman in rural Sind, or Bengal, Malawi or Niger.

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Their fate, the World Health Organisation published some recent figures, is dire and worsening. What does the Cambridge professor have to offer? It is a question you could fire at most social researchers, and most of them would fail a test of utility. For many of them failure would not matter much. But Dasgupta's subject matter is life, and death: the urgency and human force of his reference points seems to demand some application.

He answers that question autobiographically. Partha Dasgupta is a Bengali, his father coming from a district in what is now Bangladesh. His recent work, he says, has been a way of coming to terms, understanding a background, a father who was clearly a potent influence, moral and intellectual. "The family assumes a large role in my way of understanding human interchange, and this explains much of the way the analysis proceeds in the book."

How bogus that could sound, he laughs: to make of economics a vehicle of self expression! "But I am increasingly realising that the ways of coming to terms with oneself are many and varied. It is an intellectual conceit of the West that the only valid channels are religion, or poetry, music and art."

So he has produced a mightily ambitious work self-consciously echoing Adam Smith, but instead of an inquiry into wealth, it is an inquiry into poverty and the lack of well being. Its scope is gargantuan. Its method is to derive axioms - such as "well-being" (a compound of income, health, liberty and literacy), and use the axioms to build what he calls a coherent intellectual construct that can encompass societies as different as Zambia's and Mexico's, linking together age of marriage, inheritance laws, and allocations within the household.

How to promote well-being? Inside a complicated book lies a stark answer: people will choose it, if . . . there is land reform, but government does not interfere too much, concentrates on water, education and infrastructure, and does not seek to back industrial winners.

Dasgupta breaks a path, puzzling his reviewers with the range of his references and the scale of his intellectual ambition, applying formal modelling to new areas, absorbing mounds of data and analysis from medicine, and anthropology as well as political theory and mainstream Anglo-American philosophy. It even manages, once or twice, a joke. The economic analysis of under-development has more or less ignored resources, says Dasgupta: "these resources appear in the literature about as frequently as rain falls on the Thar."

Why an economic approach? "The subject is flexible yet disciplined, you can avoid being a waffler, yet accommodate in a sympathetic way a wide variety of situations.

"The models are like a design - stare at it and it can start to look different. If you are successful, you can give the reader an interpretation different from that which meets the eye. A good model should encourage us to seek new data out: for example to encourage the World Bank to obtain data on fertility rates in households, and the extent to which local environments have been degraded."

Explanations by reference to "customs" will not do. "Sociologists and anthropologists sometimes fail to see that a lot of values are instrumental: what function do dowries have? And a lot of values are common across societies. I am arguing, I suppose, that in some deep sense people are similar, that they are programmed for self-preservation, family." This is where delineating the proper sphere of government and the state in third world countries becomes exceedingly difficult. "It is not just a public-private sector issue. It is to do with a sense of where is the zone in which I should be allowed to do what I want to do, where do I have extended obligations to others, to my children?" Dasgupta clearly has much more to offer his discipline - glittering academic prizes lie ahead. But what does he offer policy-makers, and through them poor people out there? He is too fastidious to offer a "message", though a vulgariser like me might be tempted to render it as female education, potable water close to the village and rural credit institutions. It is not so much less government as different government. Governments ought to be restricted to guaranteeing civil rights, providing a legal system, along with water, sanitation and primary health care, action that could be financed by cuts in military budgets, he says - a transfer between the worlds of men and that of women of a magnitude and significance it would take more than rational persuasion from a Cambridge academic to accomplish.

David Walker is the BBC's urban affairs correspondent.

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An Inquiry into Well-Being and Destitution, Oxford University Press. Pounds 39.50 and Pounds 14.99.