The term doublethink was pioneered by George Orwell in his dystopian masterpiece 1984. In it, an alternate England is enslaved by the totalitarian Party, headed by the omnipresent Big Brother.
To maintain power, the Party invents Newspeak, a reductionist language that eliminates the ability to express complex thought.
Doublethink is the result: the ability to believe two contradictions without question. In 1984, doublethink is everywhere: citizens believe they’ve been perpetually at war with another country one day, perpetually at peace the next. It’s also present in the Party’s slogan: “War is peace. Freedom is slavery. Ignorance is strength.”