- "Qualitative difference": a change so obvious even unaided human perception can spot it.
But what about differences that are only obvious to people in the know? The difference between this
is obscure to my parents, but clear to me, for instance.
A simple and I think honest answer is that knowledge is indeed a perceptual aid. Call qualitative differences which require knowledge to detect, Simonian differences. (This is after Herbert Simon's studies of the excellent acquired intuitions of e.g. firefighters and chess grandmasters.) Thus:
- Nas vs Slightly Remastered Nas: quantitative
- Nas vs Rakim: Simonian qualitative
- Nas vs Big Pun : qualitative