When does sauce on bread become a "cheeseless pizza"?
When does a pile of stones become a "broken wall"?
For the first i'd guess when it looks like it's on it's way. For the second i'd guess when it once was. But those answers are contradictory.
The names then seem to be comparitive to how we view things, ala "half full" or "half empty".
I'm sure there's a secret to life within.