Whether it is possible to reconstruct the past definitively or not depends upon whether there is a single cause or condition that gives rise to a present state or whether there are many possible past causes or conditions that give rise to a given present state. The diagram on the left portrays an information-destroying situation in which many past causes (or conditions) correspond to a given present state. The diagram on the right portrays an information-preserving situation in which only one past cause (or condition) corresponds to a present state. Adapted from Sober, Reconstructing the Past,
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