Beginning with Warren Buffett’s multibillion-dollar gift to the Bill and Melinda Gates Foundation in 2006 and Bill Gates’s decision to turn his primary attention to giving all of that money away, philanthropy has been a hot topic in business circles. The promise has been that philanthropy would benefit from the overdue application of bu siness methods, and would therefore get faster, tougher, smarter. The Gates Foundation — the largest philanthropy not only today, but ever — is at the center of this movement, which has also been fueled by the efforts of a host of recently successful entrepreneurs, many from the worlds of finance or Silicon Valley, who seek to follow in the footsteps of Andrew Carnegie and John D. Rockefeller.

Matthew Bishop and Michael Green call this movement “philanthrocapitalism,” and it is the subject of their new book. Mr. Bishop was the principal author of a superb Economist magazine 2006 “survey of philanthropy,” and “Philanthrocapitalism” (Bloomsbury, 304 pages, $27) elaborates on that report. It outlines what the authors call a new “golden age” of philanthropy — by their count, the fifth such golden age since modern philanthropy began in late-16th Century Britain.

It is unseemly, of course, to carp about philanthropy, no matter how much its performance may fall short of its promise. After all, the best philanthropy has demonstrably saved billions of lives and much great work goes on today, more philanthropy is almost certainly better than less, and even minimal progress on social problems is preferable to none. The same is likely true of writing about the field: A shortfall in hardheaded thinking is still better than no thinking at all. Yet, however unseemly such a reaction, this much-anticipated book is a bit disappointing.

There are some significant strengths here: Mr. Bishop and Mr. Green present a nice history of their five golden ages, and are particularly good in providing transatlantic perspective to a field that is too often not just American-centric but actually provincial. They also do a very solid job of laying out the basic tenets of philanthrocapitalism, and offer a detailed, even exhaustive survey of its leading players, building on Joel Fleishman’s “The Foundation: A Great American Secret,” published last year. They wisely point out philanthropy’s limits — the Buffett gift will yield perhaps one dollar per year for each of the world’s poor — and the resulting imperative of leverage, the need to recruit allies from outside of philanthropy with greater resources that can be brought to bear.

In their account of contemporary giving, Mr. Bishop and Mr. Green are determinedly uncynical, and well sum up philanthropy’s most significant advantages: the license to “think long-term, to go against conventional wisdom, to take up ideas too risky for government, to deploy substantial resources quickly when the situation demands it — above all, to try something new.” The authors wisely add that “the big question is, will [the philanthrocapitalists] be able to achieve their potential?”

And thus we come to this book’s shortcoming. This question is posed on page 12 — and then essentially re-posed five pages before the book’s ending. In the interim, the authors have not assembled sufficient evidence to adequately answer the question. Avoidance of cynicism is admirable, but skepticism is the essence of journalistic inquiry, and skepticism seems sometimes to be missing here.

The authors, like Mr. Fleishman before them, rightly stress that philanthropy must become more transparent, more candid, more willing to admit mistakes and thus to learn from them. But many of the examples they cite seem not to heed these injunctions. When Mr. Gates’s efforts to reform American education are given a grade of “C” by Business Week, the authors report that “Gates is convinced that he deserves a higher grade,” but nowhere do they indicate which evaluation seems more persuasive. An effort called “Ed in ’08” is touted as designed “to put nationwide education reform at the heart of the 2008 presidential election,” but the failure of such an effort must have been clear even before the book went to press.

Ted Turner’s 1997 billion-dollar (in the event, as Time Warner stock fell, actually $600 million) gift to support the United Nations is described at length. But Mr. Bishop and Mr. Green seem to simply accept Mr. Turner’s own verdict that “I think the U.N. is stronger today than it was then. I just feel it is stronger.” Does that judgment square with the Iraq war, or “oil for food,” or Darfur?

Much of the strength of the philanthrocapitalism movement lies in the effort to remodel the philanthropic paradigm, and to offer a new vocabulary, a new mind-set, and new mechanisms for approaching traditional work. Reform of the philanthropic sector was, no doubt, long overdue. But the risk of advocating philanthropcapitalism without skepticism is that the movement could devolve into something like Tom Lehrer’s old joke about the new math: that it could become more important to “understand what you’re doing rather than to get the right answer.”

Mr. Tofel is general manager of the non-profit, philanthropically-supported ProPublica, a new investigative journalism newsroom. He was previously vice president and general counsel of The Rockefeller Foundation.