从句 主句

　　(1)与过去事实相反 had+过去分词 should(第一人称)would(其它人称)+have+过去分词与现在事实相反 一般过去式(动词be用were) would/should/could/might+动词原型与将来事实相反 过去式或should/were+动原 would/should/could/might+动词原型

　　(2)It is (high/about/the)time……谓语动词用过去式 指现在或将来的情况 表示早该做某事而现在已经有点晚了

　　(3)It is the first(second/third)time后的that从句中，谓语动词要用完成体来表示一种经验

　　(4)as if/though 的虚拟要点

　　1)对当时事实的假设，从句谓语用过去式，be动词一律用were

　　2)对过去事实的假设，从句谓语用过去完成式

　　3)对未来事实的假设，从句谓语用would+动词原型

　　(5)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.

　　(6)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.

　　(7)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.

　　(8)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.

　　(9)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.