The theme of reality vs. unreality is explored through the all-consuming, totalitarian power that the Party is shown to wield over its people. Again and again, Winston is confronted with issues that the Party says are "true," but that he knows are not true, such as when Oceania shifts allegiance in the war and Winston and everybody else at the Ministry of Love have to spend days changing all printed records to ensure that the historically documented "truth" matches up with the new political realities of alliances in the war. The conflict of this novel can perhaps be best summed up as one man desperately fighting to cling on to what he knows is true and not true, but eventually succumbing to accepting Big Brother's version of reality and unreality. Note how this issue is directly addressed in the following quote:
In the end the Party would announce that two and two made five, and you would have to believe it. It was inevitable that they should make that claim sooner or later: the logic of their position demanded it. Not merely the validity of experience, but the very existence of external reality was tacitly denied by their philosophy.
This occurs in Book I Chapter 7, and concerns the psychological manipulation of the Party, and is based on a very simple equation. If our worldview is something that exists only in our minds, and the Party controls our minds, then the Party actually controls the worldview that we all have, and can therefore manipulate any aspect of it, even those that we feel are most obvious and cannot be altered in any way. The Party, to show its power, the quote suggests, will indeed to go on to change simple sums because "the logic of their position demanded it." The Party by its very existence "tacitly" denies "external reality," and the reader, like Winston, is plunged into a world where what is "real" and "unreal" are no longer safely separated into recognisable categories.