There have been others explaining why “If P, then Q. Q. Therefore, P.” isn’t what is going on here, and why postdictions are not so bad.
But I’d like to address another issue: there are a lot of historical examples where all the major evidence for a hypothesis was a postdiction, but the hypothesis was so simple and fit the data so well that it became accepted mainly on the power of the postdictions. The most famous example was Kepler’s model of the solar system using ellipses. Based to a large extent on their postdictive power, the basic elliptical model was largely accepted before Newton gave an explanation for why it worked. This example isn’t perfect because the model did provide further confirmation by later astronomical observations.
There have been others explaining why “If P, then Q. Q. Therefore, P.” isn’t what is going on here, and why postdictions are not so bad.
But I’d like to address another issue: there are a lot of historical examples where all the major evidence for a hypothesis was a postdiction, but the hypothesis was so simple and fit the data so well that it became accepted mainly on the power of the postdictions. The most famous example was Kepler’s model of the solar system using ellipses. Based to a large extent on their postdictive power, the basic elliptical model was largely accepted before Newton gave an explanation for why it worked. This example isn’t perfect because the model did provide further confirmation by later astronomical observations.