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     The time-axis fallacy, also known as the Falk phenomenon, is a common misconception that relates to the concept of cause-and-effect.  Most people understand and accept the fact that the outcome of an event can affect the outcome of a later event, but that it cannot actually affect another outcome that has already happened.  However, people who accept the time-axis fallacy also assume that the knowledge of an event’s outcome cannot be used to determine the probability of the occurrence of a previous event.  These people incorrectly assume that knowledge of the outcome of the later event is completely irrelevant in determining the probability of the previous event’s outcome.

     For example, assume there are three events, A, B, and C that occur in that order.  Because of their chronological ordering, the outcome of Event B can affect the outcome of Event C, but not the outcome Event A.  However, if we know the outcome of Event B, but not the outcome of Event A, we can use our knowledge of Event B to gain a better understanding of what Event A’s probable outcome was.  People who accept the time-axis fallacy will claim that Event B’s outcome is totally irrelevant in determining the probable outcome of Event A.

*Link to the Bayes' Theorem Lesson Plan that addresses this misconception.