Doublethink was a satire/parody of communist "dialectical materialism" - in turn a development of Hegelian dialectics and finally of Heraclitus. Orwell is embarassingly simpleminded in accounting for this, and it's a crying shame he wasn't acquainted with Whitehead and Bergson and other thinkers that were fully aware that reality is process rather than essence.

Bonus: Heraclitus on Wikiquote: https://en.wikiquote.org/wiki/Heraclitus