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According to Reichenbach's account, predictive knowledge is not knowledge that one or more event will occur in the future or that a probability (i.e., a frequency or a series of similar events that occur as a certain percentage of a total) will continue to hold for the future. This results from his premise that a statement about the future cannot be uttered with the claim that it is true, because one can imagine that the contrary will happen. I argue that if anything is to count as predictive knowledge, it is the knowledge that frequent repetitions of similar events are subject to numerical regularities (i.e., his inductive posit). This sort of knowledge provides a basis for predicting the future, because it presupposes a regularity in nature, such that what may hold for the future can be inferred from knowledge of the past.
The problem of induction counts as the central objection to Reichenbach's account. Induction is unjustified, because his inductive posit, whose justification counts as a justification for induction, is itself justified by induction. In other words, induction is used to justify the claim that induction will continue to be successful in the future, which is a circular form of reasoning. His solution involves the idea of a posit, i.e., a statement which we treat as true although we do not know that it is so. Induction cannot be justified by proving that it will lead to true conclusions, but only that it will lead to good posits. Induction is justified, because it is the best method available for predicting the future, and this is so, because it leads to good posits. Reichenbach's account is open to two criticisms. First, his solution to the problem of induction is either (a) not a justification for induction, but for the use of induction, which is different sort of justification altogether, and thus still leaves his account subject to the problem of induction, or (b) it is circular. For if induction is justified because it leads to good posits, then it must also lead to his inductive posit, whose justification counts as a justification for induction. Second, there is a dilemma that weakens his account. If his inductive posit is particular, then it cannot be used to derive predictive statements. If it is translated as general, then either the result is the same, because it is falsifiable (for frequencies are subject to irregularities within relatively short periods of time), or it applies only to contexts where series of events continue for very long periods of time, in which case the posit is useless for all practical purposes. |