Who controls the past controls the future. Who controls the present controls the past.
This Party slogan appears twice in the novel, once in Book One, Chapter III, when Winston is thinking about the Party’s control of history and memory, and once in Book Three, Chapter II, when Winston, now a prisoner in the Ministry of Love, talks to O’Brien about the nature of the past. The slogan is an important example of the Party’s technique of using false history to break down the psychological independence of its subjects. Control of the past ensures control of the future, because the past can be treated essentially as a set of conditions that justify or encourage future goals: if the past was idyllic, then people will act to re-create it; if the past was nightmarish, then people will act to prevent such circumstances from recurring. The Party creates a past that was a time of misery and slavery from which it claims to have liberated the human race, thus compelling people to work toward the Party’s goals.
The Party has complete political power in the present, enabling it to control the way in which its subjects think about and interpret the past: every history book reflects Party ideology, and individuals are forbidden from keeping mementos of their own pasts, such as photographs and documents. As a result, the citizens of Oceania have a very short, fuzzy memory, and are willing to believe anything that the Party tells them. In the second appearance of this quote, O’Brien tells Winston that the past has no concrete existence and that it is real only in the minds of human beings. O’Brien is essentially arguing that because the Party’s version of the past is what people believe, that past, though it has no basis in real events, has become the truth.