So long as nuclear weapons exist, there will always be some chance of their use. It is impossible to think clearly about avoiding nuclear war without thinking in terms of probability and risk. Even efforts to abolish nuclear weapons could raise the risks of nuclear use under some political conditions. Most people do not believe that any objective would justify the loss of half a billion lives or the end of life itself. But many would be willing to raise the likelihood of major nuclear war from one chance in ten thousand to one chance in a thousand if that were necessary to preserve their way of life, or to avoid a conventional World War III. Some risks are unavoidable if we want to lead certain types of lives. At the personal level, we accept that fact whenever we enter an automobile. But we should try to reduce unnecessary risks as much as possible.