Why is it essential for the Party to rid the language of synonyms and antonyms in 1984?
The Party would claim that the purpose for this is to stop the use of words that are unnecessary. In fact, it makes things clearer, less ambiguous, and simpler for the people. Isn't that thoughtful of the Party? The people even believe this about the principles of Newspeak.
However, in truth, what this actually does to a society is dumb them down. When vocabulary has limits placed on it, the ability to have an awareness of the world decreases. Words are the colors to thought and intellect. Much like textures and colors, words can meet quite near the same thing, but not exactly something else.
For example, you can't just become untremendous in your job. That negation of a positive word feels like a fruitless meaning. You could be told you are doing mediocre, or you are slacking. Each of these provide a specificity for why you are no longer tremendous. But this is the Party's true aim, to get people to stop thinking because it is easier to control a people who do not think.
In part one, chapter five, Syme tells Winston that it is necessary to get rid of all synonyms and antonyms in the English language. Syme says that this must be done for practical reasons; there is no point in having an opposite of a word since the opposite is already contained in the word's meaning:
After all, what justification is there for a word which is simply the opposite of some other word? A word contains its opposite in itself.
While Syme gives this practical and simplistic explanation for removing synonyms and antonyms, the Party has a more sinister reason for their removal. For the Party, the whole point of Newspeak is to make "thoughtcrime" an impossibility. By stripping down language to its bare bones, the Party eradicates the possibility of free thought. A person cannot claim that the Party is "bad," for instance, if the word "bad" no longer exists.
By removing these essential words, the Party tightens its grip over the people of Oceania.