Gamblers often bet on things where the outcome has already occurred. Perhaps a pretty lady is walking by, and they bet on whether she is married. The bet may involve odds as well. So, what does it mean if someone says that he thinks it is 70% that she is married? She either is or isn’t. Some will say that 70% is a measure of his certainty. Another possibility is that he is saying that if he encountered 1000 women with the exact same looks and under the exact same circumstances, he would expect about 700 to be married. But either explanation describes a different kind of probability than the one you would use if you were speculating whether a single girl will marry in the next five years. Exactly how different is a subject that even mathematicians still debate. But some people take the position that you can’t even use probability when it comes to events that already happened, or even things like contests where the more skilled will always win (and the only uncertainty is which contestant that is). Those people are wrong.