One can predict many of the issues, large and small, that the next mayor will confront, from the city's pension liability to its penchant for saving parking spaces with patio furniture. Other crises will be as unpredictable as a once-in-a-generation recession or a baseball team that goes from winning the World Series to being defeated by a Division II college. Much of the course of a leader's tenure depends less on promises made than on qualities possessed. Electing an executive is about assessing not only platforms and positions, but the people behind them.

Given Philadelphia's rich experience with corruption and its discontents, integrity should figure prominently among mayoral attributes. While the Nutter administration has achieved a marked improvement in ethical standards and policies, recent revelations of self-dealing and quid-pro-quo politics among the city's judges and state representatives show the corrupt past isn't even past. Voters should be wary of any candidate who has shown tolerance for violations of the public trust.

Independence is a related and similarly indispensable quality. An effective mayor must be willing to buck a variety of special interests to serve the city's. Candidates who are too reliant on or reliable for any given group need not apply. Labor and business have plenty of determined advocates in town; we don't need another one in the mayor's office.

Experience also ranks high in the consideration of a candidate for any important job, and leading one of the nation's largest cities is no entry-level opportunity. The challenges ahead, many of them difficult fiscal decisions, are daunting enough without a need for crash training on how City Hall works. Intimate and substantial experience with city government is a major advantage, if not a prerequisite, for the next mayor.

Understanding of City Hall must be leavened by the political acumen to do something about it. Voters should consider the candidates' records - or lack thereof - of working with friends and foes alike to reach a goal. Cajoling and corralling City Council presents one of the greatest potential hurdles for the mayor. It has been a weakness of Mayor Nutter's tenure as much as it was a strength of that of his predecessor, John Street.

Before Street, Ed Rendell exemplified another critical mayoral trait in his pessimism-defying vision of Philadelphia as a great city replete with arts and culture. In a different manner and time, Nutter has advanced a vision of a city whose institutions and infrastructure are prepared to take advantage of an urban renaissance. The current field of candidates has not exactly exuded what George H.W. Bush once called "the vision thing." Fortunately, those who would be the next mayor still have time to capture the electorate's imagination.