The simplest notion is that probability is a measure of our credence or belief that something will happen. When we say there is a 50 percent chance of heads on the next coin toss, that is not a statement about the coin; it is a description of our belief about the result of tossing the coin. These are called Bayesian probabilities. When we say the Bayesian probability for rain tomorrow is 0 percent, that is just a way of saying we believe it will not rain, and when we say that probability is 100 percent, that says we are sure it will. Probabilities between them, such as 20 percent, 50 percent,
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