Sentence:  The Party intellectual knows in which direction his memories must be altered; he therefore knows that he is playing tricks with reality; but by the exercise of DOUBLETHINK he also satisfies himself that reality is not violated. The process has to be conscious, or it would not be carried out with sufficient precision, but it also has to be unconscious, or it would bring with it a feeling of <WSD>falsity</WSD> and hence of guilt. 
Meaning of the word marked with <WSD> tags:  The characteristic of being untrue.