打下这题目，想起上周末陪女儿去图书馆借的那本《没头脑和不高兴》，是不是很像？内心偷笑十秒钟。。。
言归正传。这篇是受群内朋友之邀写的。刚好最近也忙，找不到好的选题。那就它吧。
刚见到这个问题，当时没时间细查，第一感觉是这样的：
default应该是“未履行”。而breach则是较为一般的用法（形态较多？），或者说有主动违反的意思（与default相比）。
感觉归感觉，还是得查字典确认。来看布莱克的说法。
default
The omission or failure to perform a legal or contractual duty; esp., the failure to pay a debt when due.
大致意思跟我的感觉差不多，omission或failure都是“应做而未做”的意思。要做的事情可能是法定义务，也可能是合同义务；当然，在合同背景下就是合同义务，也就是“未履行合同义务”，最典型的就是欠钱不还。
除了作名词，它还可以作动词，相关意思如下：
1. To be neglectful; esp., to fail to perform a contractual obligation.
嗯，再次印证了上面的感觉。
再看breach：
A violation or infraction of a law, obligation, or agreement, esp., of an official duty or a legal obligation, whether by neglect, refusal, resistance, or inaction.
违反的对象也不限于合同，还包括法律、义务，尤其是违反职责或法定义务，而且形态多样，包括：疏于履行、拒绝履行和未履行。这点好像跟我的感觉也差不多。另外，violation有“主动”的意思在里边。
再看一下Osborn's词典：
default
To make default is to fail in some duty; e.g., to pay a sum due.
嗯，default是“未履行义务”，跟布莱克差不多。
美国《第二次合同法重述》的说法：
A breach may be one by non-performance, or by repudiation, or by both.
也说明breach的形态比default要多。
词典的解释大概就是这样，我们看下例句吧。
Any dispute, controversy, difference or claim (each, a “Dispute”) arising out of or relating to this Agreement, or the interpretation,breach, termination or validity hereof, shall be resolved at the first instance through consultation between the parties to such Dispute.
Confidential Information is in or becomes part of, the public domain other than through abreach of this agreement or an obligation of confidenceowed to the Disclosing Party.
Either party may terminate the Agreement by notice in writing to the other Party if the other Party isin material breach of the Agreementand theParty in breachfails to cure such breach within ten (10) business days following written notice of the relevant breach.
Each party recognises that itsbreach or threatened breach of this Agreementmay cause the other irreparable harm, and that the other may therefore be entitled to injunctive or other equitable relief.
Nothing in these terms will apply to the extent that its application would resultin a breach of applicable law or regulations.
Interest on Default
If the Subscriber does not pay an amount due under this agreement on time, it will bein default.
The failure to require performance of any provision will not affect our right to require performance at any other time after that, nor will a waiver by us of anybreach or default of these Terms, or any provision of these Terms, be a waiver of any subsequent breach or default or a waiver of the provision itself.
The Consenting Parties each acknowledge that nothing in this deed or any of the transactions contemplated by this deed constitutes (1) abreach of any term of the Shareholders Agreement, or (2)anevent of defaultunder the Shareholders Agreement.
Each of the events or circumstances set out in the following sub-clauses of this Clause 21(other than Clause 21.15(Acceleration)) is anEvent of Default.
No failure or delay on the part of Buyer to exercise any of its rights in respect of anydefault under the Contractby Supplier shall prejudice Buyer’s rights in connection with the same or any subsequent default.
The Developer shall not have committed an act of Bankruptcy prior to the date of such closing, provided Developer is alsoin material default of its obligationsunder the Development Services Agreement.
If BBB isin defaultfor any reason to make payment on time, AAA may demand immediate payment of the entire remaining unpaid loan amount.
Supplier has no knowledge of anyviolation or defaultwith respect to any order, writ, injunction or decree of any court or any governmental authority that may result in any such materially adverse effect or such impairment.
这些例句是我随手从公司翻译的文件中检索来的，大致反映了两个词在实践中的一些用法。初看起来好像很乱，两个词交替使用的场合较多。
除了上面列举的之外，还有一些我没放上来。从浏览的资料来看，我的感觉是：
(1) breach属于较为一般的用语，动作形态较多，且含有“主动违反”的意思，与之相比，default带有“消极不履行”的含义。
(2) default比较侧重于不履行金钱债务的一面，因此有interest on default这种较为专门的说法。
