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Natural kinds are secondary substances for Aristotle and so a fundamental feature of reality. Yet these natural kinds are most importantly (and as far as I know, exclusively!) biological species.

I think this is very strange on the face of it. To plagiarize from Jerry Fodor:

I suppose that sooner or later the physicists will complete the catalogue they've been compiling of the ultimate and irreducible properties of things. When they do, the likes of spin, charm, and charge will perhaps appear on their list. But catness surely won't; being a cat simply doesn't go that deep.

In the original quote it wasn't "catness" but "aboutness/intentionality". Yet, I am much more open to such mental phenomena being fundamental features of reality than the species felis catus!

And the problem doesn't stop with this prima facie implausibility:

It is an empirical fact that species evolved, species are not fixed and eternal, as Aristotle believed. We simply know that cat doesn't need to beget cat. So how can species be natural kinds? How can they be so fundamental?

And if we cannot answer this, can Aristotle's metaphysics still be salvaged? How can we disentangle it from its flawed assumptions about biology?

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    Natural kinds in biology were defended recently by Kripke and Putnam. They don't have to be irreducible or even intrinsic, Aristotle's metaphysics can survive downgrading them to relationally delineated derived classes, as long as those are objectively grounded. Dupre in Natural Kinds and Biological Taxa finds even that problematic:"I will assume the interpretation of biological taxonomy most favorable to Putnam's theory, and show that even this is often not as Putnam needs it to be". – Conifold Jan 5 '17 at 21:32
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    See Natural kinds : "Despite its long history and intuitive appeal, the conception of species as natural kinds is difficult to sustain while also maintaining a traditional view of what a natural kind requires". In other words, if we have to consider evolutionism (a concept totally foreign to Arsitotle's thought) maybe we have to conclude that cat is not a natural kind. – Mauro ALLEGRANZA Jan 5 '17 at 21:32
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    Aren't you switching the historical order? Aristotle's metaphysics was largely abandoned in the 17th century, 200 years before his biology was abandoned. – Ram Tobolski Jan 5 '17 at 23:16
  • @RamTobolski: I try to study philosophy in its historical order, and I'm stuck now with Aristotle. I want to be fair to his metaphysics from which I only heard dismissive things. Yes, it was abandoned in the early modern period, but just because it fell out of fashion doesn't mean it was flawed. I kind of think (?? maybe I post a question about this, too) that modern physics like quantum mechanics and general relativity are less hostile to Aristotle's ideas than classical physics, but one cannot say that about modern biology. Aristotle's ideas about species seem surely very, very bad. – wolf-revo-cats Jan 12 '17 at 20:24
  • @wolf-revo-cats You may be interested in the following book, which finds a lot of value in Aristotle: Retrieving Aristotle in an Age of Crisis – Ram Tobolski Jan 12 '17 at 22:37
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Some metaphysical investigation of universal kinds are flawed by the self-contradictory fallacy that Mauro quotes above "Despite its long history and intuitive appeal, the conception of species as natural kinds is difficult to sustain while also maintaining a traditional view of what a natural kind requires", contradictory because in the sciences from which the definition now arises, the very fact that it has a long history demonstrates that it has not proven in the least bit difficult to sustain.

The biological definition of species (which is the field in which we accept species evolve) is a pragmatic definition and works perfectly well for biologists to be able to communicate to each other and make predictions which have a high chance of being accurate (i.e that two animals of a different 'species' are unlikely to naturally interbreed, that two animals of a similar Genus had a similar evolutionary heritage).

This is different from the metaphysical question of whether the universe can definitely be divided into a series of separate 'things' by any universally objective means. To this end, whether a cat can breed with a dog, or whether a cat will at some point in the future, no longer have the features it has, is not really relevant. The metaphysical investigation can have no practical application without being circular (concluding, for example that a thing can be called a cat, because we call it a cat).

The more pragmatic Scientific Realism that developed from an application of the concept of natural kinds holds that such divisions, whilst being based on scientific hypotheses, reflect a universal truth, that being evident by the fact that predictions based on those divisions will apply at all times in all possible universes. As this has so far proven to be accurate (different species do not regularly interbreed naturally, bacteria with distinct DNA sequences do not spontaneously develop sequences identical to a different species), then such divisions are pragmatically true features of the universe.

Essentially, species can be fundamental natural kinds because hypotheses about one species will not apply to another, all the while predictions based on these hypotheses continue to be accurate, we can say that the distinction of these natural kinds is a truth.

  • I am afraid, I do not follow how we get from pragmatically useful to universal truth in all possible worlds in the fourth paragraph. We can also say that "seafood" and "vegetables" work for their purpose, but they are not natural kinds. As I understand, the challenge is that the usual approach of taking fundamental objects of our best theories as real does not work here because biological taxa are not fundamental in any meaningful sense of the word. But what you describe as an alternative seems to be too permissive to even distinguish natural and artificial kinds. – Conifold Jan 8 '17 at 0:23
  • @Conifold We don't, I'm asserting that, to the Pragmatist, there is no better definition of a universal truth than one which continues to produce accurate predictions. I'm saying that there is no need for a more fundamental definition of Natural Kinds, nor could anyone ever arrive at anything more useful than the definitions we have other than through the scientific process by which we derived the former. In this sense, biological taxa are precisely fundamental in the only meaningful sense, the one in which some utility can be derived from such distinction. – Isaacson Jan 8 '17 at 9:16

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