很多同学在大学英语四级考试中会存在一些误区，认为语法不那么重要，其实英语语法是学习英语的指南，也会为我们大大地提高英语，以下是小编给大家整理的大学英语四级考试语法基础：时态，希望可以帮到大家
1. 现在完成时、过去完成时以及将来完成时之间的区别
1) 现在完成时：
① 构成：have / has +过去分词
② 语法意义及要点：
a. 现在完成时表示一个过去开始的状态或动作持续到现在并可能继续持续下去，常同表示一段时间的状语连用。如so far， up to now， since， for a long time等。
--he has worked as a teacher for many years.
--up till now， nothing has gone wrong.
b. 现在完成时表示一个过去发生的对现在仍有影响的动作或事件。常与不确定的过去时间状语连用，如yet， just， before， recently等;也同表示频度时间状语连用，如often， ever， never， sometimes， several times等;还可同包括现在时间在内的时间状语连用，如now， today， this morning等。但不能同特定的过去时间状语连用(last year ， in 1997等)。
--i have never learned japanese before.
--we have been quite busy lately (recently)。
c. 在时间或条件状语从句中，当表示将来完成时的意义时，要用现在完成时来代替将来完成时。
--we’ll start at 5 o’clock if it has stopped raining by then.
--i shall go to see you when i have finished my homework.
note： 行为不能持续的瞬间动词(instantaneous verb)， 如arrive， begin， come， go， start， leave， die， join等通常不能用于这一语法意义，即该类动词在现在完成时中不能与表示一段时间的状语连用。
--he has joined the army for five years. (误)
--he has been in the army for five years. (正)
2) 过去完成时：
① 构成：had +过去分词
② 语法意义及要点：
过去完成时表示某一动作或情况发生在过去某一时刻之前并持续到该时刻。
--david and jenny had known each other for a long time before their marriage.
--they had got everything ready before the party began.
note： 与现在完成时截然不同的是过去完成时可以与表示具体过去的时间状语连用。
--he said that he had seen her the day before yesterday.
3) 将来完成时：
① 构成：shall / will + have +过去分词
② 语法意义及要点：
将来完成时表示某一动作在将来某一时刻或将来某一动作之前已经完成或发生。
--he will have graduated from high school before his next birthday.
--the shop will have closed already before you get there.
2. 哪些动词不能用于进行时
1) 表示状态的动词，如be， seem， appear， become， get等。
he is being a used-car dealer.(误)
he is a used-car dealer.(正)
she is seeming always about to smile.(误)
she seems always about to smile.(正)
2) 表示感官感觉的动词，如see(看见)， hear(听见)，feel(感觉出)， taste(尝出)，smell(闻到)等。
the medicine is tasting bitter. (误)
the medicine tastes bitter. (正)
i was seeing a car passing by our house. (误)
i saw a car passing by our house. (正)
3) 表示拥有的动词，如have， own， possess， belong， contain， hold等。
he is owning a luxurious car. (误)
he owns a luxurious car. (正)
the book is belonging to her. (误)
the book belongs to her.(正)
4) 表示思想状况、态度的动词，如believe， think， know， understand， agree， approve， consider， expect， forget， guess， hesitate， hope， imagine， mean， realize， remember， suppose， trust， want， wish等。
i’m thinking that he is right. (误)
i think that he is right. (正)
i’m understanding your feelings. (误)
i understand your feelings. (正)
5) 表示情感、愿望的动词，如admire， appreciate， care， enjoy， like， love， hate， detest， regret等。
he is loving his daughter very much. (误)
he loves his daughter very much. (正)
i’m regretting to say we cannot come. (误)
i regret to say we cannot come. (正)
3. 时态的呼应
时态的呼应又称时态一致(sequence of tenses)，指的是某些从句里的动词谓语时态必须和主句里的时态保持一致。
如果主句里的谓语动词是过去时态(过去时或过去完成时)，那么从句的谓语动词时态也相应地要用过去时。时态的呼应主要发生在间接引语和宾语从句中，但其他从句有时也存在时态一致的问题。
--he explained that he had learned chinese for many years.(现在完成时变为过去完成时)
--he said he had been collecting materials on that subject for a long time.(过去进行时变为过去完成进行时)
--he told me that they would have completed that project by the end of the year.(将来完成时变为过去将来完成时)
虽然主句用了过去时等，如果从句表示的是科学真理、客观事实或某人(物)的经常性特点时，其时态可以不必遵守时态呼应的规则而仍用一般现在时。
--galileo proved that the earth revolves round the sun.
--the teacher told the students that knowledge is power.
如果从句中有一个表示绝对过去时间的状语，就不必把一般过去时变为过去完成时。
--he said that he joined the red army in 1933.
