Plato's joints

Plato’s often-quoted statement in the Phaedrus that we should “cut up each kind according to its species along its natural joints” (265e) has become an influential metaphor in discussions of natural kinds and natural properties. In this essay, I investigate the source domain of the metaphor, the joints of the animal body, to determine if these joints are indeed “natural”—meaning that there exists a single, non-disjunctive account of joint-hood applicable to the osteological world. By examining animal joints from the perspective of both the butcher and the biologist, I argue that there is no single natural division of the body into component skeletal parts. I conclude by considering what impact this result should have on our understanding of natural kinds and on the metaphors we use to describe them.