Green is Simpler than Grue ∗

Goodman’s grue-bleen paradox relies on the claim that the predicate “green” is not simpler than the predicate “grue”, and that, for that reason, the choice between them is arbitrary. It is argued that this claim can only be made in a restricted model, in which functions have primitive names but particular values do not. In more natural models, which allow values to have proper names as well, the paradox disappears. 1 Goodman’s grue-bleen paradox Goodman’s grue-bleen paradox (Goodman, 1955) can be described as follows. Assume that a scientist wishes to test the theory that emeralds are green, contrasted with the theory that they are blue. Testing one emerald after the other, she concludes that emeralds are indeed green. Next assume that another scientist comes along, and wants to test whether emeralds are grue as opposed to bleen. “Grue” emeralds are emeralds that appear to our eyes green if tested until time T , but appear blue if they are tested after time T . “Bleen” emeralds are defined symmetrically. Choose a time T in the future, and observe that the scientist will find all emeralds to ∗I wish to thank Orna Harary, Philippe Mongin, Dov Samet, David Schmeidler, and Teddy Seidenfeld for comments. No endorsement of content should be inferred from this acknowledgment. †Tel-Aviv University, HEC, and Cowles Foundation, Yale University. [email protected]