 A seemingly obvious idea, here, is that there must be something inherently wrong with predicates such as \(blite\) or \(blurple\) (and perhaps non-raven and non-black, too) and thus a principled way to rule them out as “unnatural”. Then one could restrict confirmation theory accordingly, i.e., to “natural kinds” only (see, e.g., Quine 1970). Yet this point turns out be very difficult to pursue coherently and it has not borne much fruit in this discussion (Rinard 2014 is a recent exception). After all, for all we know, it is a perfectly “natural” feature of a token of the “natural kind” water that it is found in one physical state for temperatures below 0 degrees Celsius and in an entirely different state for temperatures above that threshold. So why should the time threshold \(T\) in \(blite\) or \(blurple\) be a reason to dismiss those predicates? (The water example comes from Howson 2000, 31–32. See Schwartz 2011, 399 ff., for a more general assessment of this issue.)