"Natural kind" is an intellectual grouping, or categorizing of things, in a manner that is reflective of the actual world and not just human interests. Some treat it as a classification identifying some structure of truth and reality that exists whether or not humans recognize it. Others treat it as intrinsically useful to the human mind, but not necessarily reflective of something more objective. Candidates examples of natural kinds are found in all the sciences, but the field of chemistry provides the paradigm example of elements. John Dewey held a view that belief in unconditional natural kinds is a mistake, a relic of obsolete scientific practices. W. V. O. Quine and Hilary Kornblith held the view that natural kinds are the unchanging structure of truth and reality. Hilary Putnam rejects descriptivist approaches to natural kinds with semantic reasoning. Hasok Chang and Rasmus Winther hold the emerging view that natural kinds are useful and evolving scientific facts. John Dewey In 1938, John Dewey published Logic: The Theory of Inquiry. He there explained how modern scientists create kinds through induction and deduction, and why they have no use for natural kinds. The philosophical issue is how humans can dependably predict that unobserved examples of a kind will have the same traits as a few observed examples. The traditional answer grew out of Aristotle's assertion that humans describe things they know in two kinds of propositions. Existential kinds—known by observing traits—are stated in "generic" propositions. Conceptual kinds—known by intuitive recognition of groups of traits—are stated in "universal" propositions. Dewey argued that modern scientists do not follow Aristotle in treating inductive and deductive propositions as facts already known about nature's stable structure. Today, scientific propositions are intermediate steps in inquiry, hypotheses about processes displaying stable patterns. Aristotle's generic and universal propositions have become conceptual tools of inquiry warranted by inductive inclusion and exclusion of traits. They are provisional means rather than results of inquiry revealing the structure of reality. Propositions as such are ... provisional, intermediate and instrumental. Since their subject-matter concerns two kinds of means, material and procedural, they are of two main categories: (1) Existential [generic means, known by induction], referring directly to actual conditions, as determined by experimental observation, and (2) ideational or conceptual [universal means, known by deduction], consisting of interrelated meanings, which are non-existential in content ... but which are applicable to existence through the operations they represent as