Double negation has two distinct forms: one indicating euphemism and the other emphasis. In the former we weaken the statement, making it milder, while in the latter we reinforce it, making it stronger and more vigorous. In other words, we aim at softening effect in the one and strengthening effect in the other.

(1) Double negation with weakening effect

A double negative in English with one of its members expressed by a negative prefix or suffix or a word implying negation (e.g. deny, blind) has the effect of euphemism. When two negatives refer to the same idea or word, they do not exactly cancel each other out in a way that is identical with a simple affirmative: “the longer expression is always weaker”. We have similar expressions in Chinese which have the same connotation as that in English.

不能不表示遗憾/不无遗憾 We cannot but regret…

难免错误 There might be some errors.

未尝不可 It might be all right. / It is not impossible.

并不否认 do not deny…

Examples:

1) He is not incapable. 他很能干。

2) We were not unprepared for the war. 我们对战争并非没有准备。

3) It not seldom happens that what seems to be impossible is made possible. 似乎不可能的事变得可能，并非少见。

Read Also: Idioms‘s translation

(2) Double negation with strengthening effect

There are many idiomatic expressions implying double negation both in English and in Chinese. In this case they are more emphatic than simple affirmatives, therefore are often found in proverbs, maxims, epigrams, antitheses, etc.

The following are some common patterns of double negation:

CANNOT…WITHOUT…; NO (NEVER)…WITHOUT…; NOTHING…WITHOUT…; NO…NO…; WITHOUT…NOTHING…; NOTHING…NOTHING…

Examples:

1. There is no right to speak without investigation.

No investigation, no right to speak. / No investigation, no say.

没有调查就没有发言权。

1) No gains without pains. / No pains, no gains.
不劳无获。

2) Nothing is impossible to a willing mind.
有志者，事竟成。/ 天下无难事，只怕有心人。

3) You can’t make something out of nothing.
无中不能生有。/巧妇难为无米之炊。

4) Do not do to others what you would not like yourself. / Do not do to others what you would not have them do to you.

己所不欲勿施于人。

CANNOT…UNLESS…; NO…UNLESS…

The double negative “cannot…without…” can be converted into another formula “cannot…unless…” :

We cannot see without our eyes. （人）没有眼睛看不见。

We cannot see unless we have eyes. （人）除非有眼睛，否则看不见。

Both mean the same thing, only “without” being a preposition while “unless” a conjunction, which means “if not” or “except when”. In Chinese, we may use such combinations as:

若无……就不…… 除非……否则…… 若非……则不……

若不……永不…… 只有……否则……

NOT…UNTIL…; NOT…TILL…

Examples

1. Health is not valued till sickness comes. 病后方知健康之可贵。

2.It was not until almost a hundred years later that such an engine was successfully built.

几乎一百年之后，才成功地制造了一台这样的发动机。