Blackwell Reference Online

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Projection from present to absent cases occurs in inductive, hypothetical and counterfactual reasoning. Goodman's grue paradox reveals that valid projection depends not only on the constitution of the evidence class, but also on its characterization ( see GOODMAN ). If all known emeralds are green, we may infer: H1: All emeralds are green but not H2: All emeralds are grue, where something is grue if examined before some future time t and found to be green, or not so examined and blue. H1 is valid, for “green” is projectible. But even though all members of our evidence class are grue as well as green, H2 is invalid since “grue” is unprojectible. A valid ampliative inference must be supported by evidence, unviolated by counterevidence, unexhausted (else it would not be ampliative), and must be framed in terms of projectible predicates. For only if a predicate is projectible can it convey credibility from known to unknown cases. How to distinguish between projectible and unprojectible predicates is a critical question for epistemology. See also   PROBLEMS OF INDUCTION . ... log in or subscribe to read full text