According to Ingsoc, the Party’s ideology, reality exists only in the mind of the individual. Do you believe external reality exists independent of perception? If a tree falls in the forest and no one is around to hear it, does it make a sound?

According to O'Brien the party can control reality simply because the brain perceives only what it is told. 2+2= anything the party wants it to be. I think that in extreme circumstances like in 1984, the external world can be controlled to a point. Fear, brain washing and behaviour modification can change how one perceives the world. People like Winston, however, search for the truth. Their intellect resists manipulation of the truth.