Friday, April 13, 2012

[PL 211] Absence of evidence & evidence of absence

The fallacy known as appeal to ignorance has two forms:
  • The fact that p is not known to be false is taken as a reason to believe that p is true.
 For example:
  1. We don't know that it is not the case that Pegasus exists.
  2. Therefore, Pegasus exists.
More schematically:
  1. We don't know that not-p.
  2. Therefore, p.
  • The fact that p is not known to be true is taken as a reason to believe that p is false.
For example:
  1. We don't know that it is the case that Pegasus exists.
  2. Therefore, Pegasus does not exist.
More schematically:
  1. We don't know that p.
  2. Therefore, not-p.
Now, suppose that one argues as follows:
  1. We don't know that it is the case that Pegasus exists.
  2. Therefore, to all intents and purposes, Pegasus does not exist.
Similarly:
  1. We don't know that it is not the case that Pegasus exists. 
  2. Therefore, to all intents and purposes, Pegasus exists.
Which of these, if any, seems like a legitimate inference to make?

      No comments:

      Post a Comment

      This is an academic blog about critical thinking, logic, and philosophy. So please refrain from making insulting, disparaging, and otherwise inappropriate comments. Also, if I publish your comment, that does not mean I agree with it. Thanks for reading and commenting on my blog.