在大学中，单独考察的题型几乎是没有的，但是语法知识点却贯穿整张试卷，下面小编为大家整理了2019年12月大学英语六级语法精析之情态动词，希望可以为大家带来帮助，一起来学习一下吧。 注意情态动词完成式的用法有两方面的含义：
1.表示已经发生的情况
(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……”