 Condillac’s reply to the Chesselden data contained the germs of an insight that was to be central for the later Treatise: the claim that visual sensations, and indeed all sensations, might contain information that goes unnoticed by a subject simply because it is not attended to. This insight, already present in the Essay, was subversive. It challenged that work’s rejection of perception by means of unconscious sensations and unconscious inferences. It led to the Treatise’s claim that having a sensation does not imply being conscious of everything that sensation involves (Treatise I.xi.8, III.iii.6). 