Natural kinds are kinds that correspond to a grouping that reflects the structure of the natural world rather than the interests and actions of human beings.

But for a kind or grouping to exist, the constituents of that grouping must be similar to each other in some way. Goodman showed that similarity is likely a vacuous concept and is context dependent by its very nature. “A is similar to B” or even “A is similar to B with respect to X” can be rephrased as “A and B both are C with respect to X.” This seems to get rid of the term entirely.

Now, given that what attribute of X one chooses to compare between A and B seems context dependent and arbitrary, how can there possibly be any kinds that are independent of human interest/motivation? Lastly, aren’t all abstract objects not directly part of the natural world? So how can there be “natural” kinds anyways?

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    Intuitively as Quine advocated judging natural kinds along with degrees of similarity are our innate flair, which is a critical evidence for scientific essentialists or realists. OTOH natural kinds may not be that scientifically objective as philosopher of chemistry Hasok Chang claimed: his examples of classification practices in chemistry confirmed the fallacy of the traditional assumption that natural kinds exist as mind-independent reality... Aug 26, 2023 at 0:10
  • Simply because Nelson Goodman claims that his rephrasing is adequate, doesn't make it so. It is open to us to deny that there are abstract properties, that brute resemblance is brute resemblance, that sets have parameters for their elements, etc. And in mathematics, we have a whole host of equivalence and similarity relations, so we could pick one of those if it were perspicuous/helpful enough. Does this escape "subjectivism"? Perhaps, perhaps not; I daresay almost nothing is totally objective or totally subjective, though, after all. Aug 26, 2023 at 0:34
  • No. Goodman's critique has been absorbed and surmounted, and similarity rehabilitated in decades after the Seven Strictures (1972). See e.g. Decock-Douven, Similarity After Goodman:"We use Tversky’s influential set-theoretic account of similarity as well as Gärdenfors’s more recent resuscitation of the geometrical account to show that, while Goodman’s critique contained valuable insights, it does not warrant a dismissal of similarity."
    – Conifold
    Aug 26, 2023 at 8:08
  • That paper, at best, argues that similarity relations can be useful. It has nothing to say on whether categories or kinds exist as a mind independent matter. Secondly, it has nothing to say about how certain seeming “natural” kinds like water are any more fundamental categories apriori than something like cars. Tversky’s set theoretic account doesn’t distinguish between these two, which arguably serves as further argument against special “natural” kinds. My question was not posed because of Goodman’s conclusion but rather his insights on how similarity seems apriori subjective.
    – user62907
    Aug 26, 2023 at 16:23


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