The New Riddle of Induction
Suppose we say that something is 'grue' if it is either
green and first observed before January 1st, 2000 or blue
and first observed on or after January 1st 2000. All emeralds so
far observed are grue: why do we not, therefore, infer that all
emeralds are grue?
Literature
The primary source is Goodman 1954, chapter III.
Note that 'grue' is sometimes also defined as "green before
2000, blue afterwards", that the definition given above is the
original one, and that some solutions to the problem only work with
the second definition, not the original one.
Copyright David Chart 1997