well with the functionally relevant [universal] groupings in nature as to make our inductions tend to come out right?" He admitted that generalizing after observing a few similarities is scientifically and logically unjustified. The numbers and degrees of similarities and differences humans experience are infinite. But the method is justified by its instrumental success in revealing natural kinds. The "problem of induction" is how humans "should stand better than random or coin-tossing chances of coming out right when we predict by inductions which are based on our innate, scientifically unjustified similarity standards." A standard of similarity is in some sense innate. This point is not against empiricism; it is a commonplace of behavioral psychology. A response to a red circle, if it is rewarded, will be elicited by a pink eclipse more readily than by a blue triangle; the red circle resembles the pink ellipse more than the blue triangle. Without some such prior spacing of qualities, we could never acquire a [classification] habit; all stimuli would be equally alike and equally different. Quine credited human ability to recognize colors as natural kinds to the evolutionary function of color in human survival—distinguishing safe from poisonous kinds of food. He recognized that modern science often judges color similarities to be superficial, but denied that equating existential similarities with abstract universal similarities makes natural kinds any less permanent and important. The human brain's capacity to recognize abstract kinds joins the brain's capacity to recognize existential similarities. Credit is due to man's inveterate ingenuity, or human sapience, for having worked around the blinding dazzle of color vision and found the more significant regularities elsewhere. Evidently natural selection has dealt with the conflict [between visible and invisible similarities] by endowing man doubly: with both a color-slanted quality space and the ingenuity to rise above it. He has risen above it by developing modified systems of kinds, hence modified similarity standards for scientific purposes. By the [inductive] trial-and-error process of theorizing he has regrouped things into new kinds which prove to lend themselves to many inductions better than the old. A man's judgments of similarity do and should depend on his theory [universal propositions], on his beliefs; but similarity itself, what the man's judgments purport to be judgments of, [is] an objective relation in the world. It belongs in the [generic] subject matter not of our [universal] theory ... about the world, but of our