Full Idea
Prima facie, it would seem that it is a least logically possible the brain state corresponding to pain should have existed (Jones's brain could have been in exactly that state at the time in question) without Jones feeling any pain at all.
Clarification
'Prima facie' means at first sight
Gist of Idea
It seems logically possible to have the pain brain state without the actual pain
Source
Saul A. Kripke (Naming and Necessity lectures [1970], Lecture 3)
Book Reference
Kripke,Saul: 'Naming and Necessity' [Blackwell 1980], p.146
A Reaction
This is Kripke's commitment to the possibility of zombies, which are only possible if the mind-body connection is a contingent one, and he shows that there are no contingent 'identities'. The answer is necessary identity, and no zombies.