這三個詞用法困擾了不少英語學習者。
「should」用來提供建議，比如「That shirt looks great on you. I think you should buy it。」。
「would」則是用來描述不可能或者虛擬的事情，比如「I would love to go to Italy, but I don't have enough money。」，這句話就是在說一件不可能發生的事。而「would」也可以表示委婉語氣，就像這句「Would you like some tea?」
「could」有三種用法：
描述過去的能力，例：「When I was younger, I could run twice as fast。」
描述將來可能發生的事，例：「If we work really hard, I think we could save up enough money for a vacation this year。」
用於禮貌請求，例：「Could I have a cup of tea?」