MIT history witnesses famous scholars who have truly founded or transformed major fields of scholarship or technology. I am confident that the current generation of MIT faculty includes many others whose contributions will prove in time to be lasting value. They set the stage for institutional excellence. How do we maintain such individual excellence as the institution progresses? I believe that the primary mechanism is the much-maligned tenure ( 终身任职 ) system. Yes, tenure. When we make the hard decision to award tenure to a colleague, we are setting the standards of the institution for the next thirty or so years, so we do so with great care and a sense of responsibility. We first give enormous choice and opportunity to new faculty members, but several years after that, the tenure system focuses our minds on a clear, informed evaluation of the quality and impact of each candidate's accomplishments in research, scholarship, teaching, and to a lesser extent, service. Many in the corporate world criticize tenure as simply job security and sinecure. But they are wrong. In a serious university, tenure is first and foremost a strong form of evaluation and accountability ( 责任形式 ). Only between 30 and 50 percent of those who enter as assistant professors are ultimately tenured. By the way, the tenure system is still justified, in my opinion, by the protection it provides against political interference in controversial ( 有争议的 ) scholarship. Undoubtedly, the system has been abused from time to time, but in first-rate institutions its implementation is one of our most important obligations, and it is a primary means for maintaining long-term excellence. To paraphrase Winston Churchill's famous characterization of democratic government, the tenure system is the worst possible academic system—except for all the others.