英语考博作文辅导班

医学考博英语语法考点之时态

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.