Full Idea
Imagine a neuroscientist who is intimately familiar with the physiology of headaches, but who has never actually experienced a headache.
Gist of Idea
A scientist could know everything about the physiology of headaches, but never have had one
Source
John Heil (Philosophy of Mind [1998], Ch.3)
Book Reference
Heil,John: 'Philosophy of Mind' [Routledge 1998], p.55
A Reaction
A more realistic version of Frank Jackson's 'Mary'. Doctors need to know that headaches are unpleasant; what they actually feel like seems irrelevant (epiphenomenal). What's it like to only have two pairs of shoes?