Raven paradox

Hempel's paradox or Rabenparadox is named after the philosopher Carl Gustav Hempel problem of epistemology. The paradox is that a universal statement about the specific objects property can be seemingly confirmed by observations of any other objects without that property. According to Hempel could, for example, the validity of the statement " All ravens are black " by the observation of a white shoe to be confirmed, which is counter-intuitive.

History

The paradox has been attributed first published in December 1940 by Janina Hosiasson linden tree in the Journal of Symbolic Logic, and Hempel, 1943, then dipped in Hempel's work A Purely syntactical definition of confirmation in the same journal on.

Formulation of the Raven paradox

After observing many ravens, which are all black, there is prima facie plausible as a sufficient justification for the inductive hypothesis: " All ravens are black ". Each additional black raven, I see, this hypothesis is further confirmed. Of course, it would be irrational to hold the hypothesis for certain, since no induction on every raven of observation is possible.

But what is when I see a non- black object that is not a raven, for example, a yellow car? The aforesaid hypothesis can give its truth value by applying logical transformation rules (in this case according to classical terminology, a contraposition ) be reworded to all non-black objects are not ravens. To formulate hypothesis seems to be confirmed by the yellow car. Since this hypothesis is logically equivalent to the initial hypothesis, thus, apparently by yellow cars the hypothesis " All ravens are black " confirmed.

Dissolution tests of the paradox

Hempel assumed that this is in the impression that this consequence is paradoxical to is a psychological misperception. The observation of non-black objects support actually a very small extent the mentioned hypothesis. Generalizing therefore support any observation which does not contradict a universal statement, this to some extent.

IJ Good proposed in 1967 before a resolution of the paradox in the article The White Shoe Is a Red Herring. He translates it the paradox in a decision problem in which, after the observation of a black raven between different possible worlds with different numbers of ravens and other objects to be selected. It shows that the reliability of an observation depends on the amount and type of deliberate hypotheses. This argument was dismissed by Hempel as irrelevant.

The proposal is similar to the hypothesis " All ravens are black " to be construed as a statement of all objects, which excludes only non-black ravens, so that red foxes confirm the hypothesis.

Starting from the question of how from the implication "If Raven, then black ," the implication "If no black, then no Raven" may be, can be checked, as in the speech of " does not contradict the claim that" finally "Support an assertion " is what ultimately the philosopher expresses his amazement. Without the " tertium non datur ," the aid of the principle of excluded middle, both transitions would not be justified. Only the speech of exclusion unschwarzer ravens would be derivable without the tertium non datur: "It can not be that there is a raven, who is not black. " [ Intuitionism ] Analogously, the talk of the yellow car that appears to the thesis of the black raven prop, as a copy of the saying " He who is not with me is against me " discernible.