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 quote occurs in Book One, Chapter VII, as Winston looks at a children’s history book and marvels at the Party’s control of the human mind. These lines play into the theme of psychological manipulation. In this case, Winston considers the Party’s exploitation of its fearful subjects as a means to suppress the intellectual notion of objective reality. If the universe exists only in the mind, and the Party controls the mind, then the Party controls the universe. As Winston thinks, “For, after all, how do we know that two and two make four? Or that the force of gravity works? Or that the past is unchangeable? If both the past and the external world exist only in the mind, and if the mind itself is controllable—what then?” The mathematical sentence 2 + 2 = 5 thus becomes a motif linked to the theme of psychological independence. Early in the novel, Winston writes that “Freedom is the freedom to say that two plus two make four.” The motif comes full circle at the end of the novel after the torture Winston suffers in the Ministry of Love breaks his soul; he sits at the Chestnut Tree Café and traces “2 + 2 = 5” in the dust on his table.