New riddle of induction

The new riddle of induction was presented by Nelson Goodman in Fact, Fiction, and Forecast as a successor to Hume's original problem. It presents the logical predicates grue and bleen which are unusual due to their time-dependence. Many have tried to solve the new riddle on those terms, but Hilary Putnam and others have argued such time-dependency depends on the language adopted, and in some languages it is equally true for natural-sounding predicates such as "green". For Goodman they illustrate the problem of projectible predicates and ultimately, which empirical generalizations are law-like and which are not. Goodman's construction and use of grue and bleen illustrates how philosophers use simple examples in conceptual analysis. Goodman defined "grue" relative to an arbitrary but fixed time t: an object is grue if and only if it is observed before t and is green, or else is not so observed and is blue. An object is "bleen" if and only if it is observed before t and is blue, or else is not so observed and is green. For some arbitrary future time t, say January 1, , for all green things observed prior to t, such as emeralds and well-watered grass, both the predicates green and grue apply. Likewise for all blue things observed prior to t, such as bluebirds or blue flowers, both the predicates blue and bleen apply. On January 2, , however, emeralds and well-watered grass are bleen, and bluebirds or blue flowers are grue. The predicates grue and bleen are not the kinds of predicates used in everyday life or in science, but they apply in just the same way as the predicates green and blue up until some future time t. From the perspective of observers before time t it is indeterminate which predicates are future projectible (green and blue or grue and bleen). In this section, Goodman's new riddle of induction is outlined in order to set the context for his introduction of the predicates grue and bleen and thereby illustrate their philosophical importance. Goodman poses Hume's problem of induction as a problem of the validity of the predictions we make.