Practical doubt

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Practical doubt is a criterion for evaluating the strength of evidence or belief. It can be used in a similar way as the saying beyond reasonable doubt, but the interpretation is slightly different.

  • Beyond reasonable doubt means that other possibilities have been carefully considered, and the conclusion from the evidence is that "a reasonable man" would find that it is unreasonable to believe that any other explanation would turn out to be true. For example, if a ship disappears in a bad storm, after some time it becomes unreasonable to think that anyone would have survived.
  • Beyond practical doubt is a different criterion and typically applies to situations with slightly smaller certainty. It means that although other possibilities are not convincingly ruled out and they may even be known to be true in some cases, it is still better to act for practical reasons as if they were not true. For example, we may know that a vaccine has a very low but greater than zero probability for severe side effects. However, the vaccine is also effective against a nasty disease. Then we may conclude that the expected benefits are so large and expected risks so small that it is advisable to take the vaccine. Therefore, a health authority can also strongly recommend the vaccine. Then, when the advice is applied on individual level, I should consider the risk of side effects to be beyond practical doubt and take the vaccine. It is important to notice that in this case side effects are not beyond reasonable doubt. If I get side effects, it should not be a surprise and I should not conclude that my decision or the advice was wrong, but instead that the unlucky and unfortunate outcome turned out to be what happened.