Each successive edition of the Newspeak dictionary has fewer words than the one before it because the Party is constantly checking the language in order to identify words that can be eliminated. Language is very important to the Party because people can only think, express themselves, associate and plan the future by using language. This is the ultimate form of mind control. If you were to remove a certain word from the dictionary, people might eventually forget the concept and stop talking and thinking about it. Therefore, by controlling their way of speaking, the Party can also control the way of thinking of the population.