The purpose of Newspeak was not only to provide a medium of expression for the world-view and mental habits proper to the devotees of IngSoc, but to make all other modes of thought impossible. It was intended that when Newspeak had been adopted once and for all and Oldspeak forgotten, a heretical thought — that is, a thought diverging from the principles of IngSoc — should be literally unthinkable, at least so far as thought is dependent on words. Its vocabulary was so constructed as to give exact and often very subtle expression to every meaning that a Party member could properly wish to express, while excluding all other meaning and also the possibility of arriving at them by indirect methods.
From the foregoing account it will be seen that in Newspeak the expression of unorthodox opinions, above a very low level, was well-nigh impossible. It was of course possible to utter heresies of a very crude kind, a species of blasphemy. It would have been possible, for example, to say Big Brother is ungood. But this statement, which to an orthodox ear merely conveyed a self-evident absurdity, could not have been sustained by reasoned argument, because the necessary words were not available. Ideas inimical to Ingsoc could only be entertained in a vague wordless form, and could only be named in very broad terms which lumped together and condemned whole groups of heresies without defining them in doing so.
George Orwell, ‘The Principles of Newspeak’,