关于“by+时间”的一个小问题

“by＋时间”的时态

“by+时间”意为“不迟于(=not later than)”;“一到(=as soon as)”；“当某时候到了[=when (the time indicated) comes]”；“到…时为止”等。时间上有过去、 现在和将来之别。主动词本身有动作与状态之分,其时态可为一般式、完成式、进行式或完成进行式。现分述如下：

1.“by＋时间”与动作性强的动词连用时，主句多用于完成式。by 后的时间可指现在、 过去或将来时间点。如： By the time he was fourteen years old, he had learned maths all by himself. 到14岁的时候，他就已经自学了数学[SB 2B p.2]。I shall have finished it by the time you come back.你回来以前我就把它做完了[1]。By the end of the match, they had kicked two goals and we had kicked four. [JB p91] 比赛结束时，他们踢进了2分我们踢了4分。They must have finished their work by this time.他们现在一定已经完成工作了[2]。

但是，上述情况中当时间为将来时，主句动作发生在从句动作之后时，主句动词可用一般时态。如：If you're not better by then, I'll take you to see the doctor. [JB3 p.85] 如果到那时还不好些，我就带你去看病。Can you finish this by tomorrow? 在明天以前你能做完这件事吗[1]？

间或有用进行式的。如：By the end of the first week the head of the department was saying very nice things about me. 第一周末时系主任给我多多美言了几句 [3]。

2.“by+时间 ”与表状态的动词连用多用于一般式。by 后时间可为现在、过去或将来时。如： By the end of the century the population numbered about four million. 到世纪末人口已经达到四百万左右[4]。You can borrow my camera, but I must have it back by five o'clock. 我的照像机你可以借去用，但是五点以前一定要还我[5]。 By the time that the security guards had realized what was happening, the gang were already inside the bank. 等到保卫人员明白过来发生了什么事时，那一伙强盗已经进了银行[5]。He ought to be here by this time /by now.他此刻（现在）应该已经来到这里了[6]。

如强调某状态在某时间前已经完成，也常用完成式。如：By next Sunday you will have stayed with us for three months. 至下星期日为止，你将与我们相聚三个月了[7]。

3.“by＋时间”与祈使句连用，用于一般式。如：Please finish the task by the end of the month.请在月底前完成这项任务[2]。Be here by this time tomorrow. 明天这个时候要到这儿[4]。

4.如强调某状态或动作在某时间为止还要继续下去，还可用完成进行式。如：By the time you graduate,I shall have been working here for five years. 到了你毕业时，我就在此地一直工作了五年之久[7]。