四六級常考語法之時態(tài)
　　1. 現(xiàn)在完成時、過去完成時以及將來完成時之間的區(qū)別
　　1) 現(xiàn)在完成時：
　　① 構成：have / has +過去分詞
　　② 語法意義及要點：
　　A. 現(xiàn)在完成時表示一個過去開始的狀態(tài)或動作持續(xù)到現(xiàn)在并可能繼續(xù)持續(xù)下去，常同表示一段時間的狀語連用。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. 現(xiàn)在完成時表示一個過去發(fā)生的對現(xiàn)在仍有影響的動作或事件。常與不確定的過去時間狀語連用，如yet, just, before, recently等；也同表示頻度時間狀語連用，如often, ever, never, sometimes, several times等；還可同包括現(xiàn)在時間在內的時間狀語連用，如now, today, this morning等。但不能同特定的過去時間狀語連用(last year , in 1997等)。
　　--I have never learned Japanese before.
　　--We have been quite busy lately (recently).
　　C. 在時間或條件狀語從句中，當表示將來完成時的意義時，要用現(xiàn)在完成時來代替將來完成時。
　　--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: 行為不能持續(xù)的瞬間動詞(Instantaneous Verb), 如arrive, begin, come, go, start, leave, die, join等通常不能用于這一語法意義，即該類動詞在現(xiàn)在完成時中不能與表示一段時間的狀語連用。
　　--He has joined the army for five years. （誤）
　　--He has been in the army for five years. （正）
　　2) 過去完成時：
　　① 構成：had +過去分詞
　　② 語法意義及要點：
　　過去完成時表示某一動作或情況發(fā)生在過去某一時刻之前并持續(xù)到該時刻。
　　--David and Jenny had known each other for a long time before their marriage.
　　--They had got everything ready before the party began.
　　Note: 與現(xiàn)在完成時截然不同的是過去完成時可以與表示具體過去的時間狀語連用。
　　--He said that he had seen her the day before yesterday.
　　3) 將來完成時：
　　① 構成：shall / will + have +過去分詞
　　② 語法意義及要點：
　　將來完成時表示某一動作在將來某一時刻或將來某一動作之前已經完成或發(fā)生。
　　--He will have graduated from high school before his next birthday.
　　--The shop will have closed already before you get there.
　　2. 哪些動詞不能用于進行時
　　1) 表示狀態(tài)的動詞，如be, seem, appear, become, get等。
　　He is being a used-car dealer.（誤）
　　He is a used-car dealer.（正）
　　She is seeming always about to smile.（誤）
　　She seems always about to smile.（正）
　　2) 表示感官感覺的動詞，如see（看見）, hear（聽見）,feel（感覺出）, taste（嘗出）,smell（聞到）等。
　　The medicine is tasting bitter. （誤）
　　The medicine tastes bitter. （正）
　　I was seeing a car passing by our house. （誤）
　　I saw a car passing by our house. （正）
　　3) 表示擁有的動詞，如have, own, possess, belong, contain, hold等。
　　He is owning a luxurious car. （誤）
　　He owns a luxurious car. （正）
　　The book is belonging to her. （誤）
　　The book belongs to her.（正）
　　4) 表示思想狀況、態(tài)度的動詞，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. （誤）
　　I think that he is right. （正）
　　I’m understanding your feelings. （誤）
　　I understand your feelings. （正）
　　5) 表示情感、愿望的動詞，如admire, appreciate, care, enjoy, like, love, hate, detest, regret等。
　　He is loving his daughter very much. （誤）
　　He loves his daughter very much. （正）
　　I’m regretting to say we cannot come. （誤）
　　I regret to say we cannot come. （正）
　　3. 時態(tài)的呼應
　　時態(tài)的呼應又稱時態(tài)一致(Sequence of Tenses)，指的是某些從句里的動詞謂語時態(tài)必須和主句里的時態(tài)保持一致。
如果主句里的謂語動詞是過去時態(tài)（過去時或過去完成時），那么從句的謂語動詞時態(tài)也相應地要用過去時。時態(tài)的呼應主要發(fā)生在間接引語和賓語從句中，但其他從句有時也存在時態(tài)一致的問題。
　　--He explained that he had learned Chinese for many years.（現(xiàn)在完成時變?yōu)檫^去完成時）
　　--He said he had been collecting materials on that subject for a long time.（過去進行時變?yōu)檫^去完成進行時）
　　--He told me that they would have completed that project by the end of the year.（將來完成時變?yōu)檫^去將來完成時）
　　雖然主句用了過去時等，如果從句表示的是科學真理、客觀事實或某人（物）的經常性特點時，其時態(tài)可以不必遵守時態(tài)呼應的規(guī)則而仍用一般現(xiàn)在時。
　　--Galileo proved that the earth revolves round the sun.
　　--The teacher told the students that knowledge is power.
　　如果從句中有一個表示絕對過去時間的狀語，就不必把一般過去時變?yōu)檫^去完成時。
　　--He said that he joined the Red Army in 1933.