The Party said that Oceania had never been in alliance with Eurasia. He, Winston Smith, knew that Oceania had been in alliance with Eurasia as short a time as four years ago. Bit where did that knowledge exist? Only in his own consciousness, which in any case must soon be anihilated. And if all others accepted the lie which the Party imposed - if all records told the same tale- then the lie passed into history and became truth. "Who controls the past," ran the Party slogan, "controls the future: who controls the present controls the past". And yet the past, though of its nature alterable, never had been altered. Whatever was true now was true from everlasting to everlasting. It was quite simple. All that was needed was an unending series of victories over your own memory. "Reality contol", they called it: in Newspeak, "doublethink".
(George Orwell's 1984)