after
1.可以说He arrived after four weeks和He arrived four weeks after（作“他在四个星期后到达了”解），但不可说He will (或would) arrive after four weeks和He will (或would) arrive four weeks after。
从某时说到多少时间以后，不该用after，该用in。所以该说He will (或would) arrive in four weeks。但说He will arrive four weeks from now和He would arrive four weeks from then也可以。
假使说“某个时刻（point of time）或日期或事件以后”，尽可用after。例如：He will (或would) arrive after four o'clock (或after 5 July，或after the ceremony).
2.说“某事件的若干时间以后”该说“若干时间after事件”，不可说after若干时间of事件，如可以说two hours after his arrival和two years after her graduation，不可说after two hours of his arrival和after ten years of her graduation。
two hours after his arrival是“他到达两小时以后”，the two hours after his arrival是“他到达以后的两小时”，for two hours after his arrival 是“在他到达以后的两小时全段时间里”，in two hours after his arrival跟没有in意思相同，within two hours after his arrival是“在他到达以后的两小时中的某时刻”。
注意下面第一句里没有the或for，第二句里有the，第三句里有for，第四句（跟第一句意思相同）里有in，第五句里有within：
- Two hours after his arrival, I called on him.
- During the two hours after his arrival, nearly a hundred people called on him.
- For two hours after his arrival, nearly a hundred people called on him.
- In two hours after his arrival, I called on him.
- Within two hours after his arrival, I called on him.
3.“若干时间after日期或月份”通常把那日期或月份除外，如five days after 3 July指从7月4日算起的5天以后，就是7月9日，five months after July指从8月算起的5个月以后，就是明年的1月。但并不一定这样，所以five days after 3 July也许指7月8日，five months after July也许在指12月。可能被人误解的时候该避免这种结构。
4.可以说After his graduation he went abroad和After his graduation he will go abroad，但不可说After his graduation he has been abroad。从过去的某时或某事说到现在，不该用after，该用since。
这里所讲的after是介词。用作连接词也是这样，所以可以说He went abroad after he graduated，但不可说He has been abroad after he graduated，这里也该把after改作since。
5.half after four, five minutes after eight等是美国英语，相当于英国英语half past four, five minutes past eight等。在英国方言里也有half after four等。
6.以after引导的状语从句里用现在时态，不用将来时态，如I shall start after he comes。不该把comes改作will come。
7.下面各句都可以说，意思相同。有人以为第二句和第四句不好。
- Having graduated, he went to Canada.
- After having graduated, he went to Canada.
- After graduating, he went to Canada.
- After he had graduated, he went to Canada.
- After he graduated, he went to Canada.
- When he had graduated, he went to Canada.
8.after通常指时间先后的次序，behind通常指位置，如August comes after July里用after，A garden lies behind the house里用behind。下面各句里的after都该改作behind。
- Don't stand after the door.
- The cat is sitting after the sofa.
- Something has got after the bush.
但往往after和behind可以通用，如Please shut the door after (或behind) you和He came in after（或behind）her。
9.be after作“追求、希求”解。例如：He is after you. （他正在找你。）和He is always after me to teach him the violin. （他老是要我教他小提琴。）注意第二句里用不定式。
10.after all有“虽然这样”的意思。例如：In coming home we got caught in the rain and became wet through and through, after all I don't mind as we had a fine time. 不可说In coming home we got caught in the rain and became wet through and through, after all I wish I hadn't joined in the outing。
