Carving Nature at Its Joints

What’s the difference between a butcher and a hack?

The expert butcher efficiently carves up a carcass in seemingly effortless motions. I’m much more the hack. Cutting up meat is tiring. I’m slow and inefficient. One might say I lack practice. I blame this on the convenience of modern day supermarkets. Meat comes prepackaged in easy to cut pieces. I much prefer this to childhood visits to the ‘wet’ market. Buckets of water were constantly splashed on the floor to wash away the blood from chickens and other assorted hunks of meat. I’m not squeamish. Seeing fowl being slaughtered in front of me isn’t a problem. But I’m lazy.

Why does the butcher’s knife-work seem effortless? In an old Taoist story, a king asks an expert butcher what his secret is. “Ordinary butchers hack their way through the animal Thus their knife always needs sharpening. My father taught me the Taoist way. I merely lay the knife by the natural openings and let it find its own way through. Thus it never needs sharpening.” This quote comes from the introductory chapter of Carving Nature at Its Joints, a collection of essays on Natural Kinds in Metaphysics and Science. The introduction, written by Matthew Slater and Andrea Borghini, is aptly titled “Lessons from the Scientific Butchery”. The book’s title alludes to Plato’s discussion of his theory of the Forms in Phaedrus. How we classify things, how we distinguish kinds from each other, is akin to “carving nature at its joints”.

Carving is a philosophy book, or rather a collection of essays by philosophers. I don’t often read philosophy. It feels like hard work with lots of definitions and seemingly twisty language. I’m more of a hack when it comes to philosophy, although I do find many of the questions posed by philosophy interesting to ruminate, particularly when they overlap with the natural sciences. So I try to hack my way through the complicated (to me) prose in the hope of learning some nuggets. I also feel humbled by my lack of knowledge in this area, and it is good for me to reminded what a struggle it can be for my students to whom the vocabulary of chemistry seems obtuse – with seemingly obscure definitions and its own twisty language.

I’ve only worked my way through the introductory chapter of Carving, but chemistry makes an appearance in several instances. The authors quote a philosopher named Nagel who writes: “The statement that something is water implicitly asserts that a number of properties (a certain state of aggregation, a certain color, a certain freezing and boiling point, certain affinities for entering into chemical reactions with other kinds of substances, etc.) are uniformly associated with each other.” Another philosopher, Quine, asserts: “Comparative similarity of the sort that matters for chemistry can be stated outright in chemical terms, that is, in terms of chemical composition. Molecules will be said to match if they contain atoms of the same elements in the same topological combinations.”

Is water H₂O, commonly depicted as a Mickey-Mouse-head-shaped molecule? A single water molecule does not have the properties that Nagel describes. A large collection of water molecules might, although those might change depending on the ‘environment’. Can you even find a sample of pure water? Students in the lab think that the deionized (dI) water is “pure” although it isn’t. Thankfully, I have never caught a student trying to chug down dI water for ‘health’ reasons. Do the different impure natural samples of water point to the Platonic Form of Water? There’s a whole book titled Is Water H₂O? by philosopher Hasok Chang. I started reading it several years back, and then got bogged down about a third of the way through. Maybe reading Carving will motivate me to get back to it. Interestingly both books have similar nondescript covers dominated by a single color. I assume red for butcher’s blood and blue for water, although these are just representations. Is blood red? Is water blue? What is color anyway?

The introduction to Carving discusses a number of philosophical definitions and positions. The concept of essence is discussed with respect to Aristotle, Locke and more contemporary philosophers such as Bealer, Kripke and Putnam. It’s been a long time since I read Aristotle or Locke, but I was reminded about the difference between primary and secondary qualities, and between nominal and real essences. I was also reminded that Aristotle wrote something called Metaphysics, which I haven’t read but probably should. (I read Nicomachean Ethics in college.) I didn’t know that Aristotle had written something called Posterior Analytics, a title which might sound naughty in this day and age.

It was interesting to learn from the authors of Carving that “chemical kinds have long been a favorite example of essentialists… it seems that quite plausible that the sort of similarity that would matter for this domain would be molecular structure: the arrangement of certain kinds of atoms.” However, the authors discuss the difficulties associated with this position and how it can be tricky to define properties. In the first week of my introductory chemistry courses, we discuss how the atom – the philosophically indivisible particle – turns out to have subatomic particles, and how the scientists discovered these particles through their properties. It’s especially ironic that the firm establishment of ‘matter is made up of atoms’ thanks to Einstein’s theory and Perrin’s painstaking experiments occurred simultaneously as Thomson, Rutherford, and others, took the atom apart.

I’m looking forward to learning more lessons from the Scientific Butchery. From the table of contents of Carving, it looks like there will be some interesting articles on fundamental physics and classifications in biology. The reading will be slow, but I’m newly motivated to put myself in the shoes of a student, and so be in solidarity with my chemistry student. Besides general chemistry, I’m also teaching quantum chemistry this semester. And no one really understands quantum mechanics. It’s a strange world with a mathematical vocabulary that many students are uncomfortable with. My comfort level with comprehending mathematical equations also has its limits, and I try to avoid the hairy parts. With strange ideas such as wave-particle duality, it becomes increasingly difficult to separate things into kinds.