|Natural Kinds, philosophy: deviating from the biological definition, substances such as gold, water, etc. are referred to as natural kinds in the recent philosophical discussion. This goes back to the way in which these terms were introduced. (See H. Putnam, “The Meaning of 'Meaning”'. In Philosophical Papers, Vol. 2. Mind, Language and Reality, Cambridge.) Starting from a primary showing, the natural kind is defined as "something like this". The decisive point here is that there is no limit to future research. Virtually, any property that is initially attributed can prove to be a false assumption. See also introduction, definitions, terms.|
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Natural Kind / necessary properties / Stalnaker: the characteristics of kangaroos are empirical, not linguistical - i.e. actual kangaroos play a necessary role - punch line: but that is not sufficient for that kangaroos necessarily are kangaroos - e.g. standard meter / Kripke: the object itself could be longer or shorter - so actual kangaroos can specify the reference of "Kangaroo", without themselves being genuine elements of the natural kind.
Natural Kind / rigidity / rigid / Stalnaker: names and natural kind terms are rigid.
Ways a World may be Oxford New York 2003