What’s the difference between stones, trees, dogs, and people on the one hand, and houses, pianos, and motorcycles on the other? According to Aristotle, the basic difference is that the things in the first group are natural things, while the things in the second are artificial things. That seems obvious, but to Aristotle, the difference goes deeper. Natural things are so called because they possess a nature that determines what they are, and how they behave. The oak tree outside my house has the nature of an oak tree. This determines how it grows, and how big it gets, and how hard the wood is. A dog has the nature of a dog, and so it barks, wags its tail, and so forth. Humans have human nature. All of these things are what they are because of something inside them.

Houses, pianos, and motorcycles, being artificial, a product of artifice, the creation of an artisan, do not have a nature. Rather, a piano is assembled from pieces; and many of these pieces are natural objects that each operate according to its own nature. Metal wire naturally vibrates and emits a tone when struck. The wood of the case naturally resonates to the tone of the wire and amplifies it. An artifact is a way of putting natural things together so that their natures all work together to achieve some desired effect.

But if artificial things don’t have a nature to call their own, they do have a property that natural things, especially living ones, generally don’t have: you can take them to pieces and reassemble them. If you take a motorcycle apart, it’s true that you no longer have a motorcycle; but if you put them back together again properly, your motorcycle is as good as new.

If you take person to pieces, on the other hand, you can’t usually reassemble them, Dr. Frankenstein not withstanding.

This distinction is often denied by the materialists among us. A human being is just atoms, they say; we can explain everything in terms of the movements of atoms. We don’t need any natures! Atoms are good enough. Given time, we’ll be able to build new people just by assembling atoms together in the right way. And yet, there’s more to being a person than just being the right set of atoms.