Grue and bleen are predicates coined by Nelson Goodman in Fact, Fiction, and Forecast to illustrate the "new riddle of induction". These predicates are unusual because their application to things is time dependent. For Goodman they illustrate the problem of projectable 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.