这三个词用法困扰了不少英语学习者。

“should”用来提供建议，比如“That shirt looks great on you. I think you should buy it。”。

“would”则是用来描述不可能或者虚拟的事情，比如“I would love to go to Italy, but I don't have enough money。”，这句话就是在说一件不可能发生的事。而“would”也可以表示委婉语气，就像这句“Would you like some tea?”

“could”有三种用法：

①描述过去的能力，例：“When I was younger, I could run twice as fast。”

②描述将来可能发生的事，例：“If we work really hard, I think we could save up enough money for a vacation this year。”

③用于礼貌请求，例：“Could I have a cup of tea?”