 Goodman  (1954)  noticed an epistemologically interesting contrast between the proposition that all emeralds are green and the proposition that all emeralds are grue (where ‘grue’ was defined to mean ‘either green and observed before \(t\) or blue and not observed before \(t\)’, for some fixed time \(t\)). Although Goodman himself does not speak in these terms, one apparent contrast relates to rationality: if one gathered many emeralds before \(t\) and observed all to be green (and therefore also grue), it would be rational to become confident that all emeralds are green, whereas it would not be rational in the same circumstances to become confident that all emeralds are  grue.[56]  Philosophers who talk about naturalness have generally seen some connection between this contrast and the fact that greenness is more natural than grueness. However, there has been little consensus about how this connection should be worked out.