英语时态的前后一致

时态的前后一致（The Sequence of Tenses）是指在说或写一段话时，通常要选一个中心时态。如果开始叙述或描写的时态着眼于“现在”，则通常以“现在”为基点从而出现下列时态的连用情况：

Our milkman usually delivers our milk at 6 o'clock every morning. It's nearly10o'clock am and the milkman still hasn't arrived. I suppose the milkman will come soon. Perhaps our milkman is ill.送牛奶的人每天早晨6点送牛奶来。现在快到上午10点了，牛奶还没有送到。我想快来了。也许是送牛奶的人生病了。
It's reported that the new railway is going to be built next year.据报道明年那里要建一条新铁路。
I expect you will have changed your mind by tomorrow.我预料到明天你就会改变主意了。
如果开始叙述或描写的时态着眼于“过去某时”，则通常以“过去某时”为基点从而出现下列时态的连用情况：

When I lived in Beijing the milkman usually delivered our milk at 6 o'clock every morning. Usually no one in our household had got up when the milk man arrived.我住在北京时，送牛奶的人每天早晨6点送牛奶来，那时我们都还没有起床。
We hadn't expected that you would come so early.我们没有料到你们会来得这么早。
She said they would have got everything ready by tonight.她说到今晚一切都会准备就绪。
“时态一致”这一概念应表述为：现在时通常与现在时连用；过去时通常与过去时连用。