  Kripke considers the identity ‘heat = molecular motion’, and holds that this is true in every possible world and so is a necessary truth. Actually the proposition is not quite true, for what about radiant heat? What about heat as defined in classical thermodynamics which is ‘topic neutral’ compared with statistical thermodynamics? Still, suppose that heat has an essence and that it is molecular motion, or at least is in the context envisaged. Kripke says (1980, p. 151) that when we think that molecular motion might exist in the absence of heat we are confusing this with thinking that the molecular motion might have existed without being felt as heat. He asks whether it is analogously possible that if pain is a certain sort of brain process that it has existed without being felt as pain. He suggests that the answer is ‘No’. An identity theorist who accepted the account of consciousness as a higher order perception could answer ‘Yes’. We might be aware of a damaged tooth and also of being in an agitation condition (to use Ryle's term for emotional states) without being aware of our awareness. An identity theorist such as Smart would prefer talk of ‘having a pain’ rather than of ‘pain’: pain is not part of the furniture of the world any more than a sense datum or the average plumber is. Kripke concludes (p. 152) that the