The third Just War requirement states: there must be serious prospects of success. This is a question concerning our certainty that we ask ourselves and others on a regular basis. If one is going to have confidence in being successful, this is a logical starting point. But what does it mean to be certain? The idea that we can be certain has been the subject of speculation for over a century (Peat in From certainty to uncertainty : the story of science and ideas in the twentieth century. Joseph Henry Press, Washington, D.C., pp. 230 2002; Dewey in The quest for certainty: a study of the relation of knowledge and action. Gifford lectures. Minton, Balch., New York, 1929). Peat [1] discusses how the concept of certainty at a fundamental level for physicists went away with the development of quantum mechanics.