What is the main theme in 1984 by George Orwell?

One way to isolate a
single central theme as a means to discuss the several topics of the novel is to point to the
notion of liberty beset by ideology in
.

While the people of Oceania are not in prison and are
free to make certain choices about how to live their lives, they are
functionally imprisoned - especially mentally.

At his
most radical,writes in his diary:

Freedom is the
freedom to say that two plus two make four. If that is granted, all else
follows.

When such a simple statement of fact
is the extreme limit of this man's mental freedom, we have to question the nature and quality of
Winston's actual liberty under his government. 's novel explores the conflict
between the individual's intellectual freedom and the interests of a totalitarian political
state - interests which necessarily oppose any and all mental
freedoms. 

Winston is not free to think and act however
he likes. He understands that the behavioral and intellectual expectations of his society
(dictated by Big Brother) are more than merely conventional norms - they are the law and they
are strictly enforced. 

Winston, like the other citizens of Oceania, is a
subject of a totalitarian regime, which is to say that he is subjected to its ideology. The aims
and posture of the Big Brother regime serve to protect the state while also defining
it.

The misinformation, reflexive moral/political justifications and the many
practices of brainwashing and enforced ignorance all also function as the character of the
government and as means to defend the integrity of that government.

This is
ideology at work in its most complete and obvious form. Set against a framework of emotional,
social and intellectual totalitarianism, the central (political) message of the novel seems to
be the suggestion that individual liberty is impossible when the very foundations of thought are
corrupted by political machinations (propaganda, cult behavior, fear mongering, etc.).

"The concept of free will, an individuals liberty to make his
or her own choices, is a threat to the totalitarian state. This is presented
throughout 1984 as free will in ones actions, thoughts, and information.
Free will encompasses not only a choice, but also a choice made on the access to true
information" .

Seen in this
light, 1984 presents a central theme of liberty imperiled by ideology. The
ideological symptoms of a totalitarian state are precisely equal in their totality as the state
is in its oppression of freedom. These symptoms are, in essence, the full and natural expression
of the political body.