“To arrange for an appointment with us, please complete the reply slip and sent it back to us.”
    上面這句話很好，很客氣，但是第二分句的動詞sent的時態(tài)不對，應(yīng)該改為send，從過去簡單時態(tài)變成現(xiàn)在簡單時態(tài)，使兩個等立分句中的動詞時態(tài)一致。
    在語法上，這叫做時態(tài)的一致（sequence of tenses）。下面是幾個指導(dǎo)原則：
    Ⅰ 主句（main clause）里的動詞是過去時態(tài)的話，名詞從句（noun clause）或副詞從句（adverb clause）里的動詞也要以過去式出現(xiàn)，如：　
    ● Tom said/ that he was busy yesterday.
    ● Janet wanted to know/ why she was not given a more important job.
    ● Lily failed/ because she did not submit the project report.
    ● None could help you/ if you continued being lazy.
    ● Although David was unwell,/ he went to office as usual.
    這原則有兩個例外，即：
    （i）當(dāng)名詞從句表達一種真理或既成事實時，其動詞時態(tài)是現(xiàn)在式，如：　
    ● Newton discovered/ that gravitation causes apples to fall.
    ● Our elders told us/ that experience is the best teacher.
    （ii）比較性的副詞從句里的動詞時態(tài)有伸縮性，視情況而定，不一定非過去式不可，如：　
    ● Susan valued his advice more/ than she values mine.
    ● Peter weighed as much/ as I shall weigh after my dinner.
    Ⅱ 主句里的動詞時態(tài)是現(xiàn)在式時，名詞從句或副詞從句的時態(tài)可以是現(xiàn)在式，也可以是其他適合的時態(tài)，如：　　　● Jim believes/ that he will get the job.
    ● The officer has just told us/that his annual leave was approved weeks ago.
    ● Christine is infuriated/ because she was criticised for her sloppy work.
    Ⅲ 形容詞從句（adjective clause）中的時態(tài)最自由，最不受拘束，如：　　● Tom mooted the idea/which some ignored, which others tend to attack, but which many will eventually accept.
    這句里的主句動詞是過去式，第一個形容詞從句的動詞雖是過去，第二個里的卻是現(xiàn)在式，第三個里的是將來式。
    最后請看看這句話：
    “President Clinton stated/ that he will not run in the next presidential election.”
    按照常理，名詞從句里的“will not run”要改為“would not run”才能和主句里的過去式“stated”一致。論者把這種現(xiàn)象視為 “特殊情況”，算是給名人的“特權(quán)”吧！一般人還是遁常道而行，避免爭議。