Two + two = five

The phrase "two plus two equals five" ("2 + 2 = 5") is a slogan used in many different forms of media, most notably in Part One, Chapter Seven of the book 1984 by George Orwell. In the novel, it is used as an example of an obviously false dogma that one may be required to believe, similar to other obviously false slogans promoted by the Party in the novel.

Orwell's protagonist, Winston Smith, uses the phrase to wonder if the State might declare "two plus two equals five" as a fact; he ponders whether, if everybody believes it, that makes it true. The Inner Party interrogator of thought-criminals, O'Brien, says of the mathematically false statement that control over physical reality is unimportant; so long as one controls one's own perceptions to what the Party wills, then any corporeal act is possible, in accordance with the principles of doublethink ("Sometimes they are five. Sometimes they are three. Sometimes they are all of them at once").

The equation 2 + 2 = 4 has been proverbial as the type of an obvious truth since the 16th century, and it appears as such in Johann Wigand's 1562 De Neutralibus et Mediis Libellus: "That twice two are four, a man may not lawfully make a doubt of it, because that manner of knowledge is grauen [graven] into mannes [man's] nature."

René Descartes' realm of pure ideas considers that self-evident idea such as two plus two equals four may, in fact, have no reality outside the mind. According to the First Meditation (1641), the standard of truth is self-evidence of clear and distinct ideas. However, Descartes questions the correspondence of these ideas to reality.

In his play Dom Juan (1682), Molière's title character is asked what he believes. He answers that he believes that two plus two equals four.

...
Wikipedia