第九讲 情态动词和虚拟语气
一、情态动词考点透析
1．can (could)，be able to。
can只有现在式can和过去式could两种形式， be able to可用于现在式、过去式、将来时、完成时。要表示“能够做某事”，可用can或be able to，但若要说过去的确运用了某种能力做成了某件事情，就只能用was/were able to，表将来具备的能力只能用will/shall be able to。
(1)If you study hard，you will be able to express freely in English in three months.
(2)The fire spread through the hotel very quickly but everyone was able to get out.
2．could是can的过去式，但是在很多情况下，特别是在口语中，它表示语气的委婉。因此，用could提问时，不能用could回答，而要用can或may。would，might用于疑问句时也表委婉语气，回答时应该用will，may。
(1)－Could I borrow your dictionary?
－Yes，of course you can.
(2)－Could I call you by the first name?
－Yes，you may.
(3)－Would you be so kind as to explain the word?
