Paul Brest, the president of the Hewlett Foundation and author of Money Well Spent announced he will be retiring in 2012. While he and I don’t see eye to eye on some core principals of philanthropy, I think that Paul embodies a number of key characteristics of a model large foundation president. I hope that Hewlett finds a replacement cut from the same cloth and that other large foundations strive to find leaders with similar characteristics.

Paul funded and personally oversaw the largest, most important philanthropy program at a major foundation. He recognized that foundations should pay just as much attention to the practice of philanthropy as they should to the execution of their programs. Unlike others, he didn’t just pay lip service to the need for constant refinement of philanthropic approach. In recent years, the Gates Foundation has ramped up its own philanthropy program, but most large foundations do not seem to believe that funding the investigation and development of the philanthropic field is their responsibility.

Paul, a former dean of the Stanford Law School, holds strong convictions about the best approaches to philanthropy. He relishes a good debate and is willing to change or modify his beliefs when presented with compelling arguments. The philanthropy blogosphere is full of what superficially passes for debate. Too often “debate” is actually just two different points of view presented over and over again without any give and take, or any modification of positions that might suggest the “debaters” are looking to build their understanding of philanthropy rather than simply seeking to win the argument.

Paul celebrated the idea that learning comes from failure. He oversaw the release of “Hard Lessons,” a major report on a Hewlett Foundation program that went off course. He also created an annual prize at the foundation for the program that made the worst grant each year. Far from trying to embarrass anyone, he intended the worst grant prize to encourage program staff to embrace and learn from their mistakes.

Paul, preparing to retire at age 72, has always recognized the value of social media to the field of philanthropy. In the 2006 Hewlett annual report, Paul discussed the need for and process of creating an online information marketplace for giving. At a time when few foundation professionals even read blogs or tracked social media, Paul took to heart my argument that if he was serious he should launch a blog as a platform for debate. A year later, he launched his own blog on the Huffington Post and engaged in a level of constructive critique that is rarely heard in public within our field.

Unlike other foundation-hosted blogs, Paul’s didn’t use this space as a digital platform for press releases. Instead, he fully understood the conversational aspect of blogging that sets it apart. He took on my arguments about how strategic philanthropy is flawed, and we engaged in discussion. He also added his thoughts to debates started by other bloggers. He reviewed important books released in the field of philanthropy. He highlighted critiques of his book by other bloggers. He criticized as “virtually meaningless” the nonprofit rating system used by Charity Navigator (but in a move demonstrating his willingness to update his believes as the evidence changes, he oversaw a grant to Charity Navigator when it sought to improve its rating approach). And he wrote a scathing indictment of the National Committee for Responsible Philanthropy’s position on how to assess foundations even while noting that Hewlett funds NCRP as part of its program to support the infrastructure of the philanthropic sector.

His belief in building knowledge through debate extended to the ranks of his own foundation. I found his public sparing with me online and at conferences remarkable, but I just about fell out of my chair when I read the Stanford Social Innovation Review article “Letting Go,” co-authored by Kristi Kimball and Malka Kopell, both Hewlett employees. The article makes a case that is at odds with the tenets of strategic philanthropy as Paul lays them out in his book. Paul easily could have discouraged the employee from publishing the piece; instead, he allowed the difference in perspective and engaged in the debate publicly.

Paul was such a great large foundation president because he saw himself as a student of philanthropy, not just a teacher. It is easy for an executive in charge of billions of dollars of philanthropic assets to assume that getting the gig must indicate that they are the one who knows what to do. But as I wrote recently, knowledge is a process not a destination.

What the field of philanthropy needs right now is senior leaders who see themselves not as the people who own the knowledge but as student-leaders striving to help the field grapple with the many, many difficult challenges it faces.