英语六级语法精析之情态动词

　　(1)must have +过去分词，表示对已发生情况的肯定推测，译为“(昨天)一定……”。如：

　　My pain must have been apparent the moment I walked into the room, for the first man I met asked sympathetically: “Are you feeling all right?”

　　(2)can’t/couldn’t have +过去分词，表示对已发生情况的否定推测，译为“(昨天)一定没……”。 如：

　　Mary couldn’t have received my letter; otherwise she would have replied before now.

　　(3)may/might have +过去分词，表示对已发生的事情做不肯定、可能性很小的推测，或事实上根本没发生，译为“也许……”。如：

　　At Florida Power’s Crystal River plant, a potentially serious leakage of radioactive water may have been unknowingly caused by an electrician.

　　2.表示虚拟语气

　　(1)needn’t have+过去分词，表示做了不必做的事，译为“其实没必要……”。如：

　　As it turned out to be a small house party, we needn’t have dressed up so formally.

　　(2)should /should not have +过去分词，表示应该做某事但实际上未做，或本不应该做但实际上做了, 译为“本(不)应该……”。如：

　　I regret having left the work unfinished; I should have planned everything ahead carefully.

　　(3)ought to have+过去分词，表示动作按理该发生了，但实际上未发生，译为“该……”，与should的完成式含义类似。如：

　　The porter ought to have called the fire-brigade as soon as he saw the fire in the stock, which went up in smoke.

　　(4)could have+过去分词，表示过去本来可以做但却未做，译为“完全可以……”。如：

　　What you said is right, but you could have phrased it more tactfully.

　　(5)may/might have + 过去分词，表示过去可以做但实际未做，译为“(那样)也许会……”。如：

　　It might have been better to include more punchy statistics and photos of equipment in the introduction to further assist first-time office automation managers.

　　3.几个情态动词常考的句型

　　(1)may/might (just) as well“不妨，最好”，与had better相近。如：

　　Since the flight was cancelled, you might as well go by train.

　　(2)cannot/can’t…too… “越……越好，怎么也不过分”。注意这个句型的变体cannot…over…。如：

　　You cannot be too careful when you drive a car.

　　The final chapter covers organizational change and development. This subject cannot be overemphasized.

　　(3)usedn’t或didn’t use to为used to (do)的否定式。

　　(4)should 除了“应该”一层意思外，大纲还规定要掌握其“竟然”的意思。如：

　　I didn’t expect that he should have behaved like that.