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Ravens Paradox

The Paradox of the Ravens was introduced by Carl Hempel in the 1940s, and has been widely discussed by philosophers, logicians and statisticians. Consider the following two principles:

EC: If EE confirms HH and HH and HH' are logically equivalent, then EE confirms HH'.

IC: Statements of the form "All FFs are GGs" are confirmed by positive instances. That is, "All FsFs are GGs" is confirmed by an aa that has both property FF and property GG.

Let HH be the hypothesis "All ravens are black", and HH' be the hypothesis "All non-black things are not ravens". Then, consider the following argument:

  1. By IC, observing a red sweater confirms HH'.
  2. HH' and HH are logically equivalent.
  3. By EC, observing a red sweater confirms HH.

But this is an absurd conclusion: It seems to suggest that you can become more certain that all ravens are black by observing objects laying around your house (e.g., a red sweater, silver computer, etc.).

Consult the following video for further discussion of the Paradox of the Ravens: