Impossibility

Impracticability

Frustration

上述单词均可用作违约之诉的辩护理由。

它们的区别在于impossibility(也称为impossibility of performance)为合同的履行不能，是合同法中一原则，指因无法抗拒的情况发生，如合同必要的执行人死亡、合同变为非法等。

impracticability为“履约的不实际性”(也称为 commercial impracticability， impracticability of performance)，它所指的范围比impossibility of performance广，包括因某种无法预见的意外事故的发生，导致履约极端困难、危险或费用太高，从而可以免除履约责任的情况，如在销售合同中，因无法预见的情况导致合同所规定的货物不存在等均属于Impracticability的范畴。

frustration为“合同受挫原则”(也称为 frustration of contract, frustration of purpose, frustration of the venture), 其是普通法一原则，指合同双方当事人均认为或合同条款规定，某物的存在为履行允诺的必要条件，在履约时如果该物因意外事故或不属于双方当事人的过失而不复存在，允诺方可免除履行允诺的义务。

Impossibility

n.

(事实的发生、存在、情况出现等之)不可能性，（合同之)履行不能(也称为Impossibility of performance)，履行不能学说(由此可免去合同的履行义务)，犯罪不能(包括事实不能犯和情况不能犯等)。

Impossibility theorem不可能定理(指美国经济计量学者阿罗的著名理论，其内容为如果众多的社会成员具有不同偏好，而社会又有多种备选方案，那么在民主制度下不可能得到令所有人都满意的结果)

Impossibility of law法律上不能犯(指缺乏基本犯罪构成要件，美国修改后的刑法对事实上不能犯和法律上不能犯未加区分，一律应予处罚，也称为legal Impossibility，true legal Impossibility)

Impossibility of performance( of contract）(合同)履行不能(可作为违约的一种辩护理由以免除违约者的责任，也称为 impossibility )

Impossibility of performance doctrine履行不能学说(指认为因不可抗力导致合同无法履行，当事人可免除违约责任之原理

Impossibility of proof证明不能(由于客观原因造成的无法证明之事)

Impossibility of relief无法获得法律救济

英文释义：

1. The fact or condition of not being able to occur, exist, or be done.

2. A fact or circumstance that cannot occur, exist, or be done.

3. Contracts. A fact or circumstance that excuses performance because(1)the obligation cannot be performed because of its nature，(2)the subject or means of performance has deteriorated, has been destroyed, or is no longer available, (3)the method of delivery or payment has failed, (4)a law now prevents performance, or(5)death or illness prevents performance. Increased or unexpected difficulty and expense do not usu. qualify as an impossibility and thus do not excuse performance.—Also termed impossibility of performance.

4. The doctrine by which such a fact or circumstance excuses contractual performance.

 5. Criminal law. A fact or circumstance preventing the commission of a crime.

——Black’s Law Dictionary

Impracticability

n.

履行艰难(指情势变化后，合同的履行尽管可能，但事实上却变得非常和不合理的艰难，即

of extreme and unreasonable difficulty，此时可免去当事人的履约责任，也称为commercial Impracticability)

 impossibility of performance履行艰难原则(有关因合同履行艰难而免去当事人履约责任的理论，涉及合同的履行不能和履行受挫。

英文释义：

1. A fact or circumstance that excuses a party from performing an act, esp a contractual duty, because( though possible)it would cause extreme and unreasonable difficulty.

2. The doctrine by which such a fact or circumstance excuses performance. 

——Black’s Law Dictionary

Frustration

n.

目的实现受阻，合同受挫原则，合同履行受挫原则(指若因预料不到的意外事件的阻挠或环境的变迁而使契约无法履行，当事人的履行义务可被解除，契约也随即被终止)

Frustration cause航程挫折条款，航程中止条款

Frustration of contract合同受挫原则

Frustration of purpose( doctrine)合同受挫原则(指法院创制的因不可预见情况而使合同签订后不能得到履行，故可对承诺人给予宽恕的原则)

英文释义：

1. The prevention or hindering of the attainment of a goal, such as contractual performance.

2. Contracts. The doctrine that if a party's principal purpose is substantially frustrated by unanticipated changed circumstances, that party's duties are discharged and the contract is considered terminated.

——Black’s Law Dictionary

（本文转自公众号“律蚁语言服务社”，已获授权）