Any object, tool, technique, or theory which is defined only as being "not this specific one".
- The set "apples" is much narrower than the set "not apples". Apples form a compact cluster in thingspace, but nonapples vary much more widely in price, and size, and use. When you say to build a wagon using "wood", you're giving much more concrete advice than when you say "not wood". There are different kinds of wood, of course - but even so, when you say "wood", you've narrowed down the range of possible building materials a whole lot more than when you say "not wood".
- Selling Nonapples, Eliezer Yudkowsky, 13 November 2008 08:10PM.