Editing Raven paradox (section)

====Distinguished predicates====
Quine<ref>{{cite book|title=Essays in Honor of Carl G. Hempel|author-link=Willard Van Orman Quine|first=Willard Van Orman |last=Quine|publisher=D. Reidel|year=1970|editor-first=Nicholas |editor-last=Rescher|location=Dordrecht|pages=41–56|chapter=Natural Kinds|display-editors=etal|chapter-url=http://fitelson.org/confirmation/quine_nk.pdf |archive-url=https://ghostarchive.org/archive/20221009/http://fitelson.org/confirmation/quine_nk.pdf |archive-date=2022-10-09 |url-status=live}} Reprinted in: {{cite book|title=Ontological Relativity and other Essays|last=Quine|first=W. V.|author-link=Willard Van Orman Quine|publisher=Columbia University Press|year=1969|location=New York|page=114|contribution=Natural Kinds}}<!---chapter=5---><!---According to Quine's foreword to the latter book (p.6 in the german translation), the reprint was issued earlier than the original.---></ref> argued that the solution to the paradox lies in the recognition that certain [[predicate (mathematical logic)|predicate]]s, which he called [[natural kind]]s, have a distinguished status with respect to induction. This can be illustrated with [[Nelson Goodman]]'s example of the predicate [[Grue and Bleen|grue]]. An object is grue if it is blue before (say) {{YEAR|{{TODAY}}}} and green afterwards. Clearly, we expect objects that were blue before {{YEAR|{{TODAY}}}} to remain blue afterwards, but we do not expect the objects that were found to be grue before {{YEAR|{{TODAY}}}} to be blue after {{YEAR|{{TODAY}}}}, since after {{YEAR|{{TODAY}}}} they would be green. Quine's explanation is that "blue" is a natural kind; a privileged predicate we can use for induction, while "grue" is not a natural kind and using induction with it leads to error.

This suggests a resolution to the paradox – Nicod's criterion is true for natural kinds, such as "blue" and "black", but is false for artificially contrived predicates, such as "grue" or "non-raven". The paradox arises, according to this resolution, because we implicitly interpret Nicod's criterion as applying to all predicates when in fact it only applies to natural kinds.

Another approach, which favours specific predicates over others, was taken by Hintikka.<ref name=Hintikka1970/> Hintikka was motivated to find a Bayesian approach to the paradox that did not make use of knowledge about the [[relative frequencies]] of ravens and black things. Arguments concerning relative frequencies, he contends, cannot always account for the perceived irrelevance of evidence consisting of observations of objects of type A for the purposes of learning about objects of type not-A.

His argument can be illustrated by rephrasing the paradox using predicates other than "raven" and "black". For example, "All men
are tall" is equivalent to "All short people are women", and so observing that a randomly selected person is a short woman should provide evidence that all men are tall. Despite the fact that we lack background knowledge to indicate that there are dramatically fewer men than short people, we still find ourselves inclined to reject the conclusion. Hintikka's example is as follows: "a generalization like 'no material bodies are infinitely divisible' seems to be completely unaffected by questions concerning immaterial entities, independently of what one thinks of the relative frequencies of material and immaterial entities in one's universe of discourse."<ref name=Hintikka1970/>

His solution is to introduce an ''order'' into the set of predicates. When the logical system is equipped with this order, it is possible to restrict the ''scope'' of a generalization such as "All ravens are black" so that it applies to ravens only and not to non-black things, since the order privileges ravens over non-black things. As he puts it:

{{quote|If we are justified in assuming that the scope of the generalization "All ravens are black" can be restricted to ravens, then this means that we have some outside information which we can rely on concerning the factual situation. The paradox arises from the fact that this information, which colors our spontaneous view of the situation, is not incorporated in the usual treatments of the inductive situation.<ref name=Hintikka1970/>}}