I have no doubt that nature has kinds which we distinguish. Some seem fairly cosmic: quarks, probably genes, possibly cystic fibrosis. Others are mundane: mud, the common cold, headlands, sunsets. The common cold is as real as cystic fibrosis, and sunsets are as real as quarks. More law-like regularities are known about mud than quarks–known to youths who play football, parents who do family laundry, and to mud engineers on oil rig sites. The regularities of mud do not have profound consequences for theoreticians. That does not make mud any the less a natural kind of stuff.”
- Ian Hacking, “The Looping Effects of Human Kinds” in Downes & Machery (eds.) Arguing About Human Nature, 2013.