Probability Is Degree of Belief
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State
A probability is a number between 0 and 1 measuring an agent's degree of belief that a claim is true — 0 certainly false, 1 certainly true.
Show
Belief 0.7 that the van has left: the van is parked or gone, fully — the 0.7 measures the believer's ignorance.
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A middle value never means partly true — the agent does not know which truth holds.