Grammar: 前/後

1. 毎日、ねる前(に)本を読む。
I read a book every day before going to bed.

2. 今日は、大学に行く前(に)家で二時間勉強した。
Today, I studied for two hours at home before I went to the university.

・Particle に is optional after 前.
・Only dictionary form before 前.
・Tense is expressed only at the very end of the sentence.
・In Ex. 2, you have the plain, non-past form before 前, even if the sentence as a whole describes a past event.

後(あと) after
3. 毎日、朝ごはんを食べた後(で)、ジョギングをする。
I jog every day after I eat breakfast.
4. 昨日は、図書館で勉強した後(で)、プールでおよいだ。
Yesterday, I swam in the pool after I studied in the library.

・particle で is optional after 後.
・only た-form before 後.
・Tense is expressed only at the very end of the sentence.
・In Ex. 3, you have the た-form before 後, even if the sentence as a whole does not describe a past event.

てから after
5. 切符を買ってから、電車に乗った。
After buying a ticket, I got on the train.

Noun + の + 前 or 後
6. アメリカ旅行の前(に)、パスポートをとった。
Before my trip to America, I got a passport.
7. 昼ごはんの後(で)、その町を見物した。
After lunch, we went sightseeing in that town.

前に before, 後で later
・に and で are NOT optional.
8. 中国には前に行ったことがある。
I have been to China before
9. 後でまた話に来ます。
I'll come to talk to you later.

Time expression + 前に or 後(ご)に
・に is NOT optional.
10. 十分前に
10 minutes ago
11. 二週間前に
2 weeks ago
12 四ヶ月前に
4 months ago **Note ヶ is pronounced "ka", not "ke", and written small.
13. 十分後(ご)に
10 minutes later
14. 二週間後(ご)に
2 weeks later
15. 四ヵ月後(ご)に
4 months later
Note: it's ごに, not あとで.