Doublethink means, according to George Orwell's dystopian novel Nineteen Eighty-Four:

the power of holding two contradictory beliefs in one's mind simultaneously, and accepting both of them. ... To tell deliberate lies while genuinely believing in them, to forget any fact that has become inconvenient, and then, when it becomes necessary again, to draw it back from oblivion for just so long as it is needed, to deny the existence of objective reality and all the while to take account of the reality which one denies—all this is indispensably necessary. Even in using the word doublethink it is necessary to exercise doublethink. For by using the word one admits that one is tampering with reality; by a fresh act of doublethink one erases this knowledge; and so on indefinitely, with the lie always one leap ahead of the truth. (pages 176-177)

As Orwell explains in The Book, the Party could not protect its iron grip on power without degrading its people and exposing them to constant propaganda. Yet knowledge of this brutality and deception, even within the Party itself could lead to disgusted collapse of the state from within, as the Soviet Union later fell in the late 20th century. For this reason, Orwell’s idealized government used a complex system of "reality control". Though the novel is most famous for its pervasive surveillance of daily life, reality control meant that the population could be controlled and manipulated merely through the alteration of everyday language and thought. Newspeak was the method for controlling thought through language; Doublethink was the method of controlling thought directly.

Doublethink was a form of trained, willful blindness to contradictions in a system of beliefs. In the case of Winston Smith, Orwell's protagonist, it meant being able to work at the Ministry of Truth deleting uncomfortable facts from public records, and then believing in the new history which he himself had written.

Through doublethink, the Party was able to not only bomb its own people and tell its citizens that the bombs were sent by the enemy, but all Party members—even the ones that launched the rockets themselves—were able to believe that the bombs were launched from outside.

Additionally, Doublethink’s self-deception also allowed the Party to maintain both huge goals and realistic expectations: "If one is to rule, and to continue ruling, one must be able to dislocate the sense of reality. For the secret of rulership is to combine a belief in one’s own infallibility with the power to learn from past mistakes" (page 177). Thus, each party member could be a credulous pawn, but would never lack relevant information. The party is both fanatical and well-informed, and thus unlikely either to "ossify" or "grow soft" and collapse. "Killing the messenger" disturbed the command-and-control of the Nazi (and later the Iraqi) militaries, but would not present itself in such a system. Doublethink thus functioned as key tool of self-discipline of the Party, to complement the state-imposed discipline of propaganda and a police state. Together, these tools hid the government's evil not only from the people, but also from the government itself, but without the confusion and misinformation associated with more primitive totalitarian regimes.

Doublethink was critical in allowing the Party to know what its true goals were without recoiling from them. Previous dictatorships made the mistake of conflating their egalitarian propaganda with their purpose; 1984 demonstrated that the next generation of dictatorship would not be so naïve.

Over the years since Nineteen Eighty-Four was published, the term Doublethink has grown to be synonymous with relieving cognitive dissonance by simply ignoring the contradiction between two worldviews. Some schools of psychotherapy such as cognitive therapy encourage people to alter their own thoughts as a way of treating different psychological maladies. See cognitive distortions.

See also: "two plus two make five," thoughtcrime, crimestop , and duckspeak