①根本违约，英文为fundamental breach，是指当事人一方迟延履行债务或者其他违约行为将导致合同相对方合同目的落空的违约方的严重违约行为。

根本违约是从英国普通法上发展出来的一种制度，其影响力之大在联合国国际货物销售合同公约、国际商事合同通则、欧洲合同法原则中均有体现。

根本违约一旦构成，产生的法律效果有二：

一是债权人可以解除债权；

二是对合同解除权的限制。

根据《联合国国际货物销售合同公约》（CISG）：a breach by one of the parties is fundamental if “it results in such detriment to the other party as substantially to deprive him of what he is entitled to expect under the contract, unless the party in breach did not foresee, and a reasonable person of the same kind in the same circumstances would not have foreseen, such a result”.

②预期违约，英文为anticipatory breach，也称先期违约，是指在合同订立后，履行期到来之前，一方表示拒绝履行合同的意图。这是英美法系特有的法律制度，大陆法系无预期违约概念。

预期违约还可以分为两种：

1，明示预期违约，即合同有效成立后至合同约定的履行期限届满前,一方当事人明确肯定地向另一方当事人表示其将不履行合同义务时,便构成根本违约,另一方当事人可以解除合同。

2，默示预期违约，与明示预期违约的不同在于，预期违约一方并没有将到期不履行合同义务的意思明确地表示出来，而是以其行为使另一方预见到其将不履行义务。

参考双语例句：

In that respect, the court based its decision on the Supreme Court judgement of 17 January 2008 (CLOUT case No. 802) which stated that “fundamental breach corresponds to the rule of fundamental breach of contract and from it is derived a system of contractual liability based on a criterion of objective imputation, attenuated, however, by exceptions — corresponding to the hypotheses of fortuitous events and force majeure under domestic law — and by a parameter of reasonableness (article 25 in fine)”; accordingly, the Navarra Provincial High Court considered that it did not appear in the case in question that any such lack of predictability of the outcome would create a situation that could be regarded as a fortuitous event or one of force majeure.

在这方面，法院的决定基于2008 年 1 月 17 日最高法庭的判决（《法规判例法》判例802）。判决指出“根本违约即为根本违反合同规则，根据此规则可推出一个以客观推定标准为依据的合同责任制度，但可以根据除外情况 ——类似于国内法关于偶发事件和不可抗力的假设——及合理性因素减轻责任（第 25 条最后）”；因此，纳瓦拉省高级法院认为，在本案中，结果可预见性的任何如此缺乏似乎都不会造成一种可视为偶然事件或不可抗力的情况。

The buyer failed to prove the fundamental breach of contract and failed to rely on a lack of conformity within a reasonable time according to Articles 38, 39 and 46 CISG.

买方未证明根本违约，且未根据《销售公约》第 38 条、第 39 条和第 46 条在合理的时限内以不符合规定为依据。