TWO AND TWO MAKE FIVE

"Two and two make five" is one of the most important sentences of the third part, it appears in the chapter twelve. It shows us how Winston had to accept that two plus two make five knowing that this is completely imposible.
Everything starts after the state found Winston with Julia, so they, to punish him, took him to a machine that gives electric shocks and the man who is controlling the machine is talking with Winston and showing him his hand with four fingers raised while asking Winston how many fingers are there. Winston is completely sure that there are just four fingers but when he says four, the man switch on the machine producing a terrible pain to Winston. However, Winston still thinks that there are just four fingers until he had a conversation with the man and for some seconds, Winston saw five fingers.
This part of the book shows us how people can change our thoughts, our mind if they have the power. Winston at the beggining was sure that two plus two make four but after the pain he felt when they used the machine, the man could convince him that two plus two make five. O'Brien tortures Winston with electroshock to show him the perception could be manipulated, to make Winston see what the Party demands one should see. So, it shows that once they have tried to change your mind and they do it, you are dead.