Full Idea
Consciousness has a first-person or subjective ontology and so cannot be reduced to anything that has third-person or objective ontology. If you try to reduce or eliminate one in favour of the other you leave something out.
Gist of Idea
Consciousness has a first-person ontology, so it cannot be reduced without omitting something
Source
John Searle (The Mystery of Consciousness [1997], Concl 2.10)
Book Reference
Searle,John R.: 'The Mystery of Consciousness' [Granta 1997], p.212
A Reaction
Misconceived. There is no such thing as 'first-person' ontology, though there are subjective viewpoints, but then a camera has a viewpoint which is lost if you eliminate it. If consciousness is physical events, that leaves viewpoints untouched.