 Following Goodman, the contrast is often summarised by saying that ‘green’ or greenness is “projectible”, and ‘grue’ or grueness is not. Projectibility is also thought of as coming in degrees, the idea perhaps being that a generalization about a more projectible property requires less evidence to make a given level of confidence rational than the corresponding generalization about a less projectible property. The difficulty of making this adequately precise, let alone of working backwards from an assignment of degrees of projectibility to a description of the rational response(s) to some given evidence, should not be underestimated (see Earman  1985  for some distinctions). But insofar as we are willing to theorise in terms of both projectibility and naturalness, we can consider the simple proposal that a property’s degree of projectibility is equal to its degree of naturalness. One worry about this (see Weatherson  2013)  is that one might want to say for other reasons that being green is much less natural than, say, being electrically charged, whereas there is no obvious sense in which it would take less evidence to be rationally convinced that all emeralds are electrically charged than that all emeralds are green.