The "Grue" Property alla Nelson Goodman

     The "grue" property is defined as:

x is grue if and only if x is green and is observed before the year 2000, or x is blue and is not observed before the year 2000.

This is a "weird" property but there is no obvious reason why we couldn't make up such a property. Now, let us pretend that the x referred to above are actually emeralds. Further, pretend that we have observed many emeralds and they have all been green and thus have had the property "grue". Then, intuitively, this should increase our belief that the next emerald we observe will be green and that it will be grue. This intuition is fine until New Years Eve in 1999. Now our pretend emeralds observed in 2000 should be grue and therefore blue and not green. Strange.......Is it still strange if we pretend x are marbles rather than emeralds.

     Why is this strange?


Goodman, Nelson. Fact, Fiction and Forecast. Indianapolis: Bobbs-Merrill, 1965.

Induction,Concepts, Uncertainty