语法大师来 CNN新闻 欧洲*试图阻止另一场负债危机中的几句话If one of these governments goes under,it could hurt all of the economies,the US economy and others worldwide.这句话中的could是什么意思?为什么不用can呢?These two leaders represent the two largest economies in Europe,they believe the new plan would prevent another major debt crisis and stablize Europe's economies.这句话中的would是什么意思?为什么不用will呢?顺便给我讲讲could和would,一直搞不清楚怎么这2个词怎么用?

could , would 在此句中均以假设语气使用
could 可能
would 将会

在这里，could和should都是情态动词，could表示某事可能会发生，should表示某人相信某事会发生
具体用法：
could：
1.MODAL能；会You use could to indicate that someone had the ability to do something. You use could not or couldn't to say that someone was unable to do something.
2.MODAL可能会；有时会You use could to indicate that something sometimes happened.
3.MODAL本能够，本可以（表示某事本有可能发生但却并未发生）You use could have to indicate that something was a possibility in the past, although it did not actually happen.
4.MODAL（表示某事可能属实或可能发生）可能You use could to indicate that something is possibly true, or that it may possibly happen.
should:
1.MODAL（表示曾经相信、希望或期待）将，将会You use would when you are saying what someone believed, hoped, or expected to happen or be the case.
2.MODAL（表示曾经打算）将，将会You use would when saying what someone intended to do.
3.MODAL（表示可能出现的情况的结果或影响）会，将会You use would when you are referring to the result or effect of a possible situation.
4.MODAL（would 或 would have 与过去分词连用，表示有充分理由认为或猜测是某种情况）肯定，一定，应该You use would, or would have with a past participle, to indicate that you are assuming or guessing that something is true, because you have good reasons for thinking it.
推荐你用科林斯辞典，里面有单词详细的用法，而且是用英文解释的

would 更能表现出人心里的意愿,常翻译为"愿意";而could更倾向于”有能力”.would在向别人提出问题时更委婉,Would you please open the door? 用would提出请求一般为大多数外国人所接受,他们会说It is my pleasure．...