The MacArthur Foundation is best known for giving open-ended "genius" grants of $625,000 to the people who brought you Hamilton and Radiolab and lots of obscure but similarly accomplished scholars, artists, and thinkers. Today the philanthropy is announcing a new plan to put $100 million behind a single big idea to solve a social problem.

If that sounds vague, it’s by design. “This is wide open,” said Cecelia Conrad, managing director of the foundation. “One of the arguments for making it agnostic is to allow the proposers to give us some sense of what $100 million will do.”

The famous MacArthur Fellowships are just a small portion of the annual giving from the foundation, which has about $6.5 billion in assets from the insurance and real estate fortune of John D. and Catherine T. MacArthur. In recent years, the foundation has focused more narrowly on a discrete set of problems, including climate change and criminal justice reform, “with the hopes of magnifying our impact,” Conrad said. The latest initiative, called $100&Change, is part of the strategy to make big bets on transformative solutions.

So what can $100 million do? It's a sliver of what pharmaceutical companies say they spend to develop a new drug, so don't expect to cure a disease. Facebook Inc. Chief Executive Officer Mark Zuckerberg put the same amount into an attempt to improve Newark's public schools, with uneven results. One of the challenges Conrad acknowledges is balancing the transformative with the achievable. There’s a danger in thinking too small or too pie-in-the-sky.

“There is a risk, and we are attempting to mitigate that risk,” Conrad said. “We are really looking for solutions that have pretty strong and persuasive evidence that they will work.”

In some ways, it’s the opposite of the “genius” fellowships, which go to bright individuals with no strings attached. While the $100 million problem can be in any area, the foundation wants proposals to meet some specific criteria. The recipient has to address something significant, not trivial. There has to be some evidence the recipient will solve it. The applicants—which can be nonprofits or businesses, but not individuals—also have to show that they’re capable of carrying out the plan. And the effect has to be durable, with a clear way to sustain results when the grant money runs out. That might mean taking a program that worked in one place and replicating it on a larger scale, or turning a prototype technology into a working product.

Grant seekers will have until Sept. 2 to register on MacArthur’s site and until Oct. 3 to submit a detailed proposal. Finalists will be selected in the summer of 2017. A panel of 28 experts from nonprofits, academia, and businesses will help evaluate the ideas. The foundation plans to award a $100 million grant for a different problem every three years. Each grant will be tied to annual milestones, said Conrad, allowing the foundation to tell by year five "whether we have achieved the impact we’re looking for."

Beyond the big idea it will fund, the MacArthur Foundation hopes the process will bring to the surface a lot of other creative proposals worthy of attention. Semifinalists will get technical assistance from the foundation to refine their ideas—and, potentially, exposure to other philanthropists prepared to write smaller checks. The goal, Conrad said, is to counter a “sense of pessimism” in the country.

“We believe that there are solutions to problems that can work, that we know about, that perhaps have been piloted, but need to be scaled up,” she said.