🚀 go-pugleaf

In article <1992Oct21.170822.1775@CSD-NewsHost.Stanford.EDU> casley@Tarski.Stanford.EDU (Ross Casley) writes:
>
>As you note, "all crows are black" and "all non-black objects are
>non-crows" are logically equivalent.  Now it is reasonable to consider a
>black crow as a small piece of evidence for all crows being black; collect
>enough such instances and no counterexamples and you can consider "all
>crows are black" as being established by observation.
>
>But by exactly the same reasoning finding a non-black non-crow should be a
>small piece of evidence supporting the proposition "all non-black objects
>are non-crows," hence it should support "all crows are black."  But this
>obviously doesn't work.  So there's something odd about this notion of
>evidence.  Either it doesn't respect logical equivalence, or it is not
>possible to tell what counts as evidence for a proposition from its
>logical form.
>
>-Ross Casley

Just for fun:

If you define the universe as containing only a fixed and finite number of
objects to which properties may be ascribed (a favorite assumption for some
CS folks of my acquaintance), then there is a very clear way in which the
observation of non-black non-crows provides support for the hypothesis 
that 'All crows are black.'


Dan Cohen

danco@philos.umass.edu
danco@titan.ucc.umass.edu