WHAT IS THE ARGUMENT ABOUT?

It is tempting to argue that if something has a very small probability we can behave as if it were impossible. When we say ‘small’ here we are usually thinking of something that is extremely small, like one in several millions. We run our lives on this principle. Every day we are subject to a multitude of tiny risks that we habitually ignore. We might be struck by a meteorite, contract the ebola virus, find a two-headed coin or forget our name. Life would come to a halt if we paused to enumerate, much less prepare, for such possibilities. Even the most determined hypochondriac would be hard put to identify all the risks we run in matters of health. Surely, then, we can safely reject the possibility of anything happening if the probability is extremely small? Actually the position is more subtle and we must be a little more careful about what we are saying.