赖世雄教你学英语语法
时态及语态
1-14：时态的前后一致
1．主句为现在时，从句除过去完成时、过去完成进行时不能用以外，其他时态皆可用
例：I think he has come.
I think he is coming.
I think he already came.
I think he will have come by the end of this month.
I think he was singing a song when I came yesterday.
I think he had come.(X)
I think he had been sleeping.(X)
I think he had been sleeping when I came.(O,因有过去时之副词从句when I came）
2.主句为过去式时，则从句不得用表现在或将来的时态，但可使用过去时、过去完成时、过去进行时、过去完成进行时。
例：I thought he was nice.
I think he had come back.
I think he would come back.
I think he was working hard.
I think he had been working hard.
I think he will come back.(X)
I think he has been working hard.(X)
3.从句表真理时，无论主句是过去、现在或将来时，该从句都用现在时。
例：They knew that the sun rises in the cast.
（他们知道太阳从东方升起。）
We know that the sun rises in the cast.
（我们知道太阳从东方升起。）
She will know that the sun rises in the cast.
（她将会知道太阳从东方升起。）