在英語復(fù)合句中，從句中的動(dòng)詞時(shí)態(tài)，特別是賓語從句中的動(dòng)詞時(shí)態(tài)，通常在一定程度上受到主句中動(dòng)詞時(shí)態(tài)的制約，英語語法上稱這種現(xiàn)象為時(shí)態(tài)呼應(yīng)。
時(shí)態(tài)呼應(yīng)一般應(yīng)遵循下列幾條原則：
一、如果主句中動(dòng)詞是過去時(shí)態(tài)，賓語從句中的動(dòng)詞時(shí)態(tài)通常是各種過去時(shí)態(tài)的一種，具體用過去時(shí)態(tài)的哪一種，則需要根據(jù)具體意義來確定。一般來說：
1．如果主句中的動(dòng)作與賓語從句中的動(dòng)作同時(shí)發(fā)生，則從句中的動(dòng)詞用一般過去時(shí)，或根據(jù)具體意義的需要用過去進(jìn)行時(shí)。如：
I knew he studied in this school．我知道他在這所學(xué)校學(xué)習(xí)過。
I knew she was studying English in this school in the years from 1985 to 1987．我知道從1985年到1987年期間她在這所學(xué)校學(xué)習(xí)英語。
2．如果賓語從句中的動(dòng)作發(fā)生在主句的動(dòng)作之前，則從句中的動(dòng)詞用過去完成時(shí)。如：
He said that he had visited his old friends．他說他已拜訪了他的老朋友。
3．如果賓語從句中的動(dòng)作在主句動(dòng)作發(fā)生前已持續(xù)了一段時(shí)間，則從句中的動(dòng)詞用過去完成時(shí)或過去完成進(jìn)行時(shí)。如：
He said that the patient had been under his treatment for three years．他說病人已在他那兒治療三年了。
I knew that he had been working here since 1960．我知道他自1960年以來就一直在這里工作。
4．如果賓語從句中的動(dòng)作發(fā)生在主句的動(dòng)作之后，則從句中的動(dòng)詞用一般過去將來時(shí)，或過去將來進(jìn)行時(shí)，或過去將來完成時(shí)。如：
He said that they would read the book the following year．他說他們下一年才讀那本書。
He said that they would be reading when she came．他說她來時(shí)他們將在閱讀。
He said that they would have finished reading the book by the first of July．他說他們到7月1日止將讀完那本書。
但是，如果賓語從句表示的是一般真理或習(xí)慣性行為，則不受時(shí)態(tài)呼應(yīng)的限制。如：
The students knew that water consists of oxygen and hydrogen．學(xué)生們那時(shí)都知道水是由氧和氫構(gòu)成的。
He told his teacher that he takes a bath once a week in winter．他告訴老師他冬天每周洗一次澡。
二、如果主句中的動(dòng)詞是現(xiàn)在時(shí)或?qū)頃r(shí)，則賓語從句中的動(dòng)詞可根據(jù)意義的需要確定任何一種時(shí)態(tài)。如：
I know that my brother has gone to Shanghai．我知道我弟弟去上海了。
I have just learned that he went to Changsha yesterday．我剛剛獲悉他昨天去了長沙。
I shall tell the doctor that my classmate vomited three times last night．我將告訴醫(yī)生我的同學(xué)昨晚嘔吐了三次。
三、定語從句及表示原因、結(jié)果、比較、讓步等的狀語從句一般不受時(shí)態(tài)呼應(yīng)的限制。如：
Now he is reading the book which I bought the day before yesterday．他正在讀我前天買回來的那本書。
He didn’t go out last night because he will have an examination tomorrow．他昨晚沒外出是因?yàn)槊魈煲▍⒓樱┛荚嚒?br />
His blood pressure was higher last year than it is this year．他的血壓去年比今年高。
四、主語從句、表語從句一般要受時(shí)態(tài)的限制。如：
What he would do was of no importance．他將做什么并不重要。
The question was what he would do next．問題是下一步他將做什么。
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