what is "doublethink"?

Doublethink

Newspeak word with two mutually contradictory meanings. The first is used to refer to an opponent, and can be defined as habitually contradicting plain facts. The second is used to refer to a Party member, and can be defined as a loyal willingness to believe contradictory statements when the Party demands it, which allows for continual alteration of the past.

http://www.gradesaver.com/1984/study-guide/glossary-of-terms/

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"Winston sank his arms to his sides and slowly refilled his lungs with air. His mind slid away into the labyrinthine world of doublethink. To know and not to know, to be conscious of complete truthfulness while telling carefully constructed lies, to hold simultaneously two opinions which cancelled out, knowing them to be contradictory and believing in both of them, to use logic against logic, to repudiate morality while laying claim to it, to believe that democracy was impossible and that the Party was the guardian of democracy, to forget whatever it was necessary to forget, then to draw it back into memory again at the moment when it was needed, and then promptly to forget it again: and above all, to apply the same process to the process itself. That was the ultimate subtlety: consciously to induce unconsciousness, and then, once again, to become unconscious of the act of hypnosis you had just performed. Even to understand the word ‘doublethink’ involved the use of doublethink."