It is certain that this bus will either be late or not late, which is a probability of 1 The missing value of a probability can be worked out by subtracting the known probabilities from 1 (100% when ...

"Yes or no: was there once life on Mars?" I can't say. "What about intelligent life?"' That seems most unlikely, but again, I can't really say. The simple yes-or-no framework has no place for shadings ...