natural kinds, but rather of reliable processes discoverable by competent induction and deduction. He replaced the ambiguous label "natural kind" by "warranted assertion" to emphasize the conditional nature of all human knowings. Assuming kinds to be given unconditional knowings leads to the error of assuming that conceptual universal propositions can serve as evidence for generic propositions; observed consequences affirm unobservable imagined causes. "For an 'inference' that is not grounded in the evidential nature of the material from which it is drawn is not an inference. It is a more or less wild guess." Modern induction is not a guess about natural kinds, but a means to create instrumental understanding. Willard Van Orman Quine In 1969, Willard Van Orman Quine brought the term "natural kind" into contemporary analytic philosophy with an essay bearing that title. His opening paragraph laid out his approach in three parts. First, it questioned the logical and scientific legitimacy of reasoning inductively by counting a few examples posting traits imputed to all members of a kind: "What tends to confirm an induction?" For Quine, induction reveals warranted kinds by repeated observation of visible similarities. Second, it assumed that color can be a characteristic trait of natural kinds, despite some logical puzzles: hypothetical colored kinds such as non-black non-ravens and green-blue emeralds. Finally, it suggested that human psychological structure can explain the illogical success of induction: "an innate flair that we have for natural kinds. He started with the logical hypothesis that, if all ravens are black—an observable natural kind—then non-black non-ravens are equally a natural kind: "... each [observed] black raven tends to confirm the law [universal proposition] that all ravens are black ..." Observing shared generic traits warrants the inductive universal prediction that future experience will confirm the sharing: "And every reasonable [universal] expectation depends on resemblance of [generic] circumstances, together with our tendency to expect similar causes to have similar effects." "The notion of a kind and the notion of similarity or resemblance seem to be variants or adaptations of a single [universal] notion. Similarity is immediately definable in terms of kind; for things are similar when they are two of a kind." Quine posited an intuitive human capacity to recognize criteria for judging degrees of similarity among objects, an "innate flair for natural kinds.” These criteria work instrumentally when applied inductively: "... why does our innate subjective spacing [classification] of [existential] qualities accord so