New Riddle of Induction, explained.
Goodman’s new riddle of induction asks which predicates are projectible when different descriptions fit the same observed evidence.
Why it happens
Observed emeralds are green before cutoff T. The green predicate and the grue predicate both fit them, but grue predicts blue for a newly observed emerald after T under the declared definition.
Goodman’s new riddle of induction asks which predicates are projectible when different descriptions fit the same observed evidence.
Read the result
Both predicates fit the observed pre-cutoff emeralds. The board displays rival projections rather than generating evidence that one colour transition actually occurs.
A worked example
Fit the same past with green and grue
Observe several green emeralds before the declared cutoff time T.
Compare the green and grue rules’ identical fit to those observations.
Consider a newly observed emerald after T and inspect their different predictions, then articulate a principle of projectibility.
OPTIONAL DEEPER DETAILGo deeper: inside the model
Inside this model
Observed emeralds are green before cutoff T. The green predicate and the grue predicate both fit them, but grue predicts blue for a newly observed emerald after T under the declared definition.
Where this idea is useful
A practical use
Make the assumptions behind extrapolation explicit instead of relying only on a history of matching examples.
A common misconception
“Any rule fitting the past is automatically as useful a projection as every other.”
The riddle asks what justifies projecting some predicates rather than others; matching observed cases alone does not provide that whole account.
What this explanation leaves out
- The display does not reveal actual colour-changing emeralds or prove every fitted hypothesis equally useful. Predicate choice and projectibility remain philosophical questions.
Is the future emerald shown changing colour at the cutoff?
No. The board compares predicate-defined predictions and does not assert a physical process or future observation that settles the philosophical issue.
What makes the description you extrapolate more projectible than an alternative that fits the same history?
Associated thinkers
Associations marked provisional are awaiting source review.
Further reading
Explore the original research or the teaching reference behind this experiment.