Full Idea
The ontology of the unconscious consists in objective features of the brain capable of causing subjective conscious thoughts.
Gist of Idea
Unconscious thoughts are those capable of causing conscious ones
Source
John Searle (The Rediscovery of the Mind [1992], Ch. 7.II.7)
Book Reference
Searle,John R.: 'The Rediscovery of the Mind' [MIT 1999], p.160
A Reaction
As it stands, this definition would fit a brain tumour. I think Searle is wrong. There is no sharp line between conscious and non-conscious brain events. Research has surely made it clear that dim brain events directly intrude into my conscious states.