 I can't believe that Steam has missed tagged as a walking simulator. I mean, genres mean something, damn it. This is a clear violation of some sort of categorical imperative. Why is a raven like a writing desk? It isn't. Ravens and writing desks have very little in common, really. There are many different ways to group things in the universe, some of which might include both. You might find a raven and a writing desk next to each other on some exhaustive list of things made of matter, things made of organic cells, black things, maybe. But some of those groupings seem like they're built on more of a shallow surface-level resemblance rather than any deep connection between the members of the group. When I gesture at a set of particular things and say, all these things are black, I've certainly created some sort of meaningful classification, but it seems arbitrary and not particularly useful. While saying something like, all these things belong to the taxonomic family of Corvide, well, that seems like it's getting at something deeper and more substantial. The philosophy of natural kinds has some overlap with the idea of universals, which we've talked a little about before. Plato's framing of the concept is still a compelling way of thinking about it. If we imagine nature or the universe like a Thanksgiving turkey, stay with me here, we could pick up a very sharp knife and cut at it any which way we please, but the goal of a good butcher, or philosopher, or scientist, or programmer, is to carve nature at the joints, to pick out particular conceptual slices that follow or echo some deeper underlying structure and break the universe into genuinely meaningful bits rather than arbitrary ones. We don't want a hack job that gets us a little meat, half a wishbone, and a bit of the table. We want a drumstick, no more, no less. Take the chemical elements, helium, carbon, potassium. These are generally taken to be a paradigmatic example of natural kinds. We could group atoms along any arbitrary boundaries we might imagine. I could say atoms to the left of me, or atoms that existed before 1918, but we find that grouping them in terms of atomic weight and electron count seems to be particularly fertile ground for successful inductive inferences, for guessing certain properties that we expect to appear in each member of the group. When I discover something about one particular carbon atom, something happening to do with its being an instance of the group, carbon atoms, I can predict that all the other carbon atoms will share the same property and probably be right, because the kind carbon atoms is taken to reflect how the universe itself delineates which particles will behave in what way. However, there are also cases where it's not so clear cut. Biological taxonomies are one of the first things you might think of for natural kinds, the arrangement of living things into kingdoms and families and whatnot, but they're notoriously squirrely. Ask a room of four biologists how to define a species and you'll get five answers. It seems readily apparent that fish are categorically different than birds, but it's hard to draw a crisp boundary in the space between them like we did with the elements. Whether you're looking at genetics or phenotypes, the space between fish and birds is filled with a gentle gradient of incremental in-between species, such that any line that's drawn is going to be something that we draw arbitrarily just to cut a meaningful distinction somewhere. There's separation, but no clear division, so we can't really call them natural kinds without some further thought. This is a bit of a problem. It suggests that at least some of the kinds that we might think of as being natural might really just be loose groupings that we draw out of convenience, mirroring our own interests and perceptions rather than the underlying structure of the universe. We don't really have concrete expectations about apparently artificial kinds. There's no expectation that groups of hatchbacks, third graders, or flags are going to be well-defined or perfectly consistent in their behavior. There are plenty of valid inferences that you might draw about each of those groups based on observation and correlations, but although we might be surprised by exceptions, there's some acknowledgement that they're to be expected. No reason to get your jimmies rustled. But the categories of physics? Find an electron that's really only three-fifths of an electron or doesn't behave like an electron all the time? That's a much bigger deal. Realism about natural kinds is essential for scientific realism, the position that scientific laws and principles are actually describing the universe as it is, not some wacky features of human cognition. When we say hydrogen boils at 20 Kelvin, we take that to be a statement about something real out there. Categorically different from a statement like music in minor key sounds sad, or this soup needs more salt. In order for any scientific law or principle to work that way, the subjects of those laws must be taken to be natural kinds. Saying hydrogen boils at 20 Kelvin requires that the label hydrogen picks out a meaningful subdivision of the universe and identifies a property that any entity within it must have as the universe itself works that way. Taking another tack, we might reject that natural kinds actually exist in any objective fashion, instead embracing a position called constructivism, which treats them more or less as human inventions or constructs, same as groups of hatchbacks or flags. They're not real categories in any sense. They don't call out any aspect of the universe that has any significance outside our heads. They just happen to be particularly useful for our purposes, a way of looking at things that tend to be advantageous for accurate inferences and predictions. From this perspective, hydrogen atoms wouldn't be any more or less a meaningful category than third graders. So long as you can manage the same quality of inference and discover things about the group by inspecting individuals in it, might as well make a periodic table of third graders. So we have these conflicting accounts about whether natural kinds exist or whether they're just instrumental explanations that happen to work well for us. That's all well and good, but why should anyone who's not particularly into philosophy really care either way? Well, the philosophy of natural kinds has implications for how we approach and think about categories, which in some ways dictates how we grasp and process information about the world. A lot of work in psychology has been put towards systems of analysis that define certain groups and sort people into those groups based on certain criteria, stuff like big five personality traits, moral foundations theory, that kind of thing. There have been questions raised as to whether these endeavors are picking out any real features of human psychology, or whether they're simply creating weird arbitrarily shaped boxes and cramming a diversity of phenomena into them just for the sake of sorting. That attitude makes a lot of sense for a natural kinds realist, someone who thinks that there's a fact of the matter about what sorts of categories will mirror the actual psychological structure of human beings. But for a constructivist, it's not so important whether the categories are made up and the points don't matter. So long as they're useful, so long as we keep looking for more useful categories, there's no value in speculating which ones are closer to the truth, whatever that means. Framing debates about policy in terms of natural kinds is also an interesting way to break them down or dissolve them into more fundamental questions. I'm sure that if you think of your favorite political controversy, you might be able to see a glimmer of the realist-antirealist debate somewhere at its core. A dispute about which ways of breaking up the world are how reality is and which are just useful ways of thinking. Can you think of anywhere else the concept might be applied? Please leave a comment below and let me know what you think. Thank you very much for watching. Don't forget to follow us, subscribe, and share. And don't stop funking.