But everything I thought I knew about hope changed when I traveled with my mother, author Frances Moore Lappé ("Diet for a Small Planet"), to write a book together. We were in search of solutions and stories -- and, as she would specify, hopeful ones. (I scoffed at her use of the word at first, but that would soon change.) We sought people who could show new ways of thinking about relationships to community, to the land, to health, to economics. We wanted to find people proving it was possible to knit these together so that values of sustainability were a part of the very fabric of life -- not an afterthought.

We knew we had to find "big" examples: nothing that would seem insignificant or marginal. We found them, everywhere.

We met Wangari Maathai and women in her Green Belt Movement, helping to avert the desert creeping south into Kenya by planting trees -- more than 40 million since the movement's humble beginnings in the late 1970s. We met farmers in India who were part of environmentalist Vandana Shiva's network, keeping productive and ecological traditional farming practices alive throughout the country. We met Bangladeshi economist Muhammad Yunus, a pioneer in the now global microcredit movement, and the women borrowers in his "bank for the poor." And we set out for the bracingly cold plains of Brazil, where we met formerly landless workers who had joined one of South America's largest social movements -- the Landless Workers Movement -- and now had a roof over their heads, land to farm and a community to belong to.

Along our journey, we met extraordinary change-makers who showed us the creative paths to real sustainability and who taught me a thing or two about hope.

For, despite their differences, everyone we met shared a common spirit. I couldn't seem to find another word for this spirit but "hope." Yet, these people weren't starry-eyed dreamers, nor in deep denial. They saw clearly that their success was not guaranteed. Indeed, many were up against some of the most daunting challenges any of us could imagine, and worse. In Brazil, for instance, the landless workers who organized faced the threat of death, with more than 1,000 landless people having already died in that struggle.

When my mother and I began the journey to write what became "Hope's Edge," I thought I knew what hope was. I thought it could be determined by a simple formula: calculating how much things were getting better, divided by how much things were getting worse. But what I learned from the amazing people we met -- and heard, in Portuguese, French, Kikuyu, Spanish, Bengali, Hindi and more -- was a powerful redefinition of hope. Hope is not what we find in evidence; it's what we discover through engaging in the world. I learned that it's possible to confront our era's daunting challenges with eyes wide open and no assurance that you will succeed, and yet still be filled with the most enlivening, energizing, empowering hope. Hope, by this definition, is more verb than noun; you become hope by taking action.