Many times double negative is used in Chinese sentences to make an affirmative effect.
Double Negative 双重否定
The affirmative effect in a double negative sentence is much stronger than in a single affirmative sentence. A double negative is adopted to strengthen or emphasize the affirmative tone.
There are three forms for double negation:
1. Two negative adverbs used in a sentence.
我得去那里。→ 我不得不去那里。
2. One negative adverb and one negative verb used in a sentence.
在中国出生的人都会说中文。→ 在中国出生的人当中没有一个不会说中文的。
3. A negative adverb or a negative verb in a rhetorical question.
我表哥的婚礼，我要去参加。我表哥的婚礼，我怎么能不去参加呢？
The following words are generally used in a double-negation structure: 不会不、不得不 、 不能不、不是不、不可能不 、 难道…不… 、 怎会不…、怎能不…、怎么会…不、 etc.