Full Idea
A system is either conscious or it isn't, but within the field of consciousness there are states of intensity ranging from drowsiness to full awareness.
Gist of Idea
A system is either conscious or it isn't, though the intensity varies a lot
Source
John Searle (The Mystery of Consciousness [1997], Ch.1)
Book Reference
Searle,John R.: 'The Mystery of Consciousness' [Granta 1997], p.5
A Reaction
I think this all-or-nothing view is the last vestiges of Cartesian dualism, and is quite wrong. Heaps of neuroscience (about blindsight, subliminal awareness, neurosis etc.) says we will never understand the mind if we think it is only the conscious part.