from 与现在完成时

对学生讲, since 短语和 since 从句与现在完成时连用, 而 from 短语不与现在完成时连用, 是可以的。例如, 《新概念英语》(第二册) 便有这方面的试题(答案为 B): Tim has been in Australia for six months. His brother hasn't seen him ____ January. A. for B. since C. from D. by

但是,英语教师则应当注意到 from 的另一种用法:from 短语与现在完成时连用,表示“从过去某时一直延续至今的动作或状态”,尤其是 from a boy, from his childhood, from an infant, from olden times 等短语:

1. They have been friends from a child. 他们从孩子时起就是朋友了。

2. She has slept eight hours from yesterday morning. 她从昨天早晨起已经睡了8个小时了。

3. I would hesitate to say that the situation has improved from last year. (AP report, 1981) 我可不愿意说从去年起情况已有了改善。

新版的PEU明确指出，from有时候也可以与现在完成时连用，尤其是在from短语含有“从一开始就……”的意思时：

She's been like that from her childhood. (或 ... since her childhood.) 她从童年时代起就是那样。

From the moment they were married, they've quarrelled. 他们从结婚的那一刻起就一直吵架。

From the dawn of civilization, people have made war. 从有人类文明以来，人们就进行战争。

[附注]此外, from ... on, 相当于 since, 亦可与现在完成时连用。此外, from ... to, from ... till 有时也与现在完成时或现在完成进行时连用:

1. The two of them have been friends from that day on (= since that day). 他们两个从那天起成了朋友。

2. We've been working from morning to night. (= without stopping) 我们从早到晚一直在工作。