Take a hypothetical world where the word "sport" is used to refer only to football, soccer, and basketball, and no other sports exist. Also assume that any new "sport" will automatically be dismissed as not one because it is none of these, including any deviation from the standard rules of the three sports.
Your idea of sport implies that concepts can be non-sports. Red is a concept that's neither a sport nor a non-sport. Red can't be a non-sport because it's no activity. If you don't give me enough knowledge to separate non-sport from concepts like red than your sport concept is useless. If you do give me that knowledge than your sport concept is well defined.
If you talk about free will on the other hand it's more difficult what you mean with non-free will. Here I think you actually define the concept of free will as something that happens in absence of causality.
A non-sport would simply be anything that is not a sport. I don't see why saying that anything that isn't football, soccer, or basketball is not a sport automatically creates a new category of non-sports other than not being a sport.
On free will, it could actually be a relatively coherent concept close to free will as we understand it (if, as with any creation of a coherent definition where there was none before, very minor alteration of the concept). A conscious being which is simultaneously an acausal force which does things for no reason whatsoever. You...
I'm not sure about this, but presenting it anyway for scrutiny.
I was thinking that it doesn't matter if a concept is undefined, or even cannot be defined, if hypothetically speaking said concept can exist without any ambiguity within it then it is still a tenable concept. The implications, if this is true, would be that it would knock down Quine's argument against the analytic-synthetic distinction.
Your thoughts, Lesswrong?