As a young academic, Martha Nussbaum received some important encouragement over a coffee in a scruffy burger bar from a fellow philosopher. He was John Rawls. "If you can influence people, you have a duty to do that," he said. No one could say she hasn't risen to the challenge. Called "philosophy's action woman" by Time magazine, Nussbaum, who is 56, has been justly described as "one of the polymaths of our age".
The intellectual range and volume of her work is remarkable; a friend of mine, who edits a philosophy magazine, said it was a full-time job simply reading all her output. At the University of Chicago, she holds appointments in the law, philosophy and divinity departments, as well as holding associate positions in the classics and political science departments. She is also an affiliate of the university's Committee on Southern Asian Studies and a board member of the Human Rights Programme. Oh yes, and the founder and co-ordinator of the Centre for Comparative Constitutionalism. She holds 22 honorary degrees. So what have you being doing with your time?
But Nussbaum is uncomfortable staying in the ivory tower (or in her case, several towers). Borrowing a phrase from Seneca, she sees herself as a "lawyer for humanity". Despite a privileged upbringing - she attended the elite Baldwin School in Bryn Mawr, Pennsylvania - her lifelong passion is to use her intelligence to help the powerless. Reading Dickens from the age of 12 onwards was one factor. "It was exhilarating to know that there was someone in the world for whom poor children mattered deeply," she has said.
If Nussbaum is influential, it is less because she has constructed a single philosophical system or framework than because she brings her philosophical and legal knowledge to bear on contemporary issues. In Sex and Social Justice (1999), she used classical notions of the good life to argue against anti-gay laws in some US states; in Cultivating Humanity: a classical defence of reform in liberal education (1997) she had defended multiculturalism in education, as well as affirma- tive action, on Socratic grounds. To Nussbaum, a full life is one in which people have the capabilities, both material and non-material, to lead lives that they have reason to value. This approach rejects both utilitarianism and libertarianism, and has strongly influenced the work of the United Nations and other development agencies.
Her career had a slow start, largely because she gave birth to her daughter at the age of 26, four years after her first marriage (and conversion to Reform Judaism). It developed more quickly when, following her divorce, she began a new relationship with the Nobel prize-winning economist Amartya Sen, with whom she spent seven years at the World Institute for Development Economics Research at the United Nations University. "It was as close to a conversion as I knew," she has said. "I went off to Finland and to India, and the whole world of issues opened up to me." She has since launched several devastating assaults on conventional development economics - with its concentration on boosting GDP at pretty much any cost - which to her mind is unhistorical, narrow and lacking in any philosophical coherence. (Her present partner is the brilliant and personable constitutional scholar Cass R Sunstein, one of America's leading public intellectuals. You'd want to be about a thousand times as well read as you are now before joining this couple for dinner.)
Writing after the events of 11 September 2001, Nussbaum urged Americans to look beyond their own borders. "We can take this disaster as occasion for narrowing our focus, distrusting the rest of the world and feeling solidarity with Americans alone. Or we can take it as an occasion for expansion of our ethical horizons. Seeing how vulnerable our great country is, we can learn something about the vulnerability all human beings share, about what it is like for distant others to lose those they love to a disaster not of their own making, whether it is hunger or flood or ethnic cleansing."
While this eloquently captures her fervent internationalism - like Diogenes, she sees herself as a "citizen of the world" - it also shows the limits of her influence. Few could claim that the US has taken a path remotely like the one for which she argued. Nussbaum is hugely influential on the world of ideas; the trouble is that the world of ideas is not hugely influential on the world in general.
Nussbaum moves with ease - some of her critics claim that too much so - between disciplines. Her latest book, Upheavals of Thought: the intelligence of the emotions (2001), contains chapters on Mahler's Second Symphony, Walt Whitman, Proust (from whom the title is taken), Spinoza, Dante, Augustine, Emily Bronte and Joyce.
To some, she can appear arrogant in her liberal certainty. "It is quite obvious that there are certain things that I think are very important," she says. "But what is important to me is the ability to give an argument for that and to listen to other people's arguments."
Martha Nussbaum holds the increasingly unfashionable views that thinking and reading are important and that philosophy has a public role. She has said that the fate of ideas rests on whether people read. For her, the notion of "eudemonia", of flourishing, at the heart of Aristotle, is the ultimate point of it all. "The failure to flourish," she has written, "is a kind of death."
Martha Nussbaum Born 1947 in New York. "Neo-stoic" political and moral philosopher. Studies the emotional underpinnings of civil society. Now Ernst Freund Distinguished Service Professor of Law and Ethics, University of Chicago. Among her numerous books are The Fragility of Goodness: luck and ethics in Greek tragedy and philosophy (1986), Sex and Social Justice (1999) and Upheavals of Thought: the intelligence of emotions (2001)