This post discusses correct use of since, after and for in English language. It is followed by a brief exercise to test your skills. Since, after and for are often confused in expressing time, these simple explanations should help you understand the differences.

Since

Since refers to a duration of time between two points in time, and usually requires perfect tenses. It must have a starting point.

For example:

They have known about the scandal since last month.

(Last month is the starting point, but they still know/it is still relevant that they know)

After

After refers to a period of time following a specific point, without a particular duration/end point.

For example:

They found out about the scandal after the news report.

(This tells us when they found out; it does not matter how long they have known for.)

 

For

For refers to a duration of time without defining a starting or finishing point.

For example:

They have known about the scandal for three weeks.

(It is not important when they found out, or if it is finished – we want to know how long they have known for.)

Exercise to practice since, after and for

Choose since, after or for for the following sentences:

1. They’ve been together ___ three weeks.
2. He hasn’t been back to Seaford ___ that time.
3. The students went home ___ lunch.
4. He’s been working in the factory ___ last year.
5. John and Bob have been working on their project ___ seven months already.
6. They have been performing music in the theatre ___ many years.
7. He has been a judge ___ more than three years.
8. They’ve been living in the apartment ___ quite a long time.
9. I haven’t seen Lucy ___ last week.
10. Maggie was stuck in the traffic jam ___ three hours.
11. These berry bushes have bloomed every spring ___ 1986.
12. Our country’s economy has been stable ___ the Olympic Games.
13. I haven’t seen her ___ a long time.
14. Many new ideas have been used ___ she replaced the old boss.
15. The noise lessened ___ eight o’clock.
16. He went to the pub ___ the show ended.
17. She’s been crying ___ yesterday.
18. He worked on the farm ___ fifteen years before he retired.
19. I haven’t seen her ___ a long time ago.
20. We’ve been waiting ___ noon.

Answers and explanations

1. They’ve been in love for three weeks. The point of the sentence is to tell us how long they have been in love.
2. He hasn’t been back to Seaford since that time. Since refers to the period of time between him going to Seaford and now.
3. The students went home after lunch. The period of time they went home for is not relevant – lunch finished and they went. 
4. He’s been working in the factory since last year. Since refers to the time between last year and now.
5. John and Bob have been working on their project for seven months already. The point is how long – seven months.
   
6. They have been performing music in the theatre for many years. The duration is important, how long – many years.
7. He has been a judge for more than three years. The duration is important, how long – three years.
   
8. They’ve been living in the apartment for quite a long time. The duration is important, how long – quite a long time.
9. I haven’t seen Lucy since last week. Haven’t refers to now, last week is the starting point, so with two points in time since is necessary.
10. Maggie was stuck in the traffic jam for three hours. The duration is important, how long – three hours.
11. These berry bushes have bloomed every spring since 1986. Have blossomed tells us it is happening now, and 1986 is a starting point, so since is necessary.
12. Our country’s economy has been stable since the Olympic Games. Has been tells us it is still stable now, the Olympic Games is a starting time, so since is needed.
13. I haven’t seen her for a long time. How long? A long time – the duration is important.
14. Many new ideas have been used since she replaced the old boss. The present perfect gives now as a point in time, when she replaced the old boss is the starting point.
15. The noise lessened after eight o’clock. We do not know, and it is not important, how long the noise lessened for, or until, we only have a starting point.
16. He went to the pub after the show ended. It is not important how long he went to the pub for, but when he went – after the show.
17. She’s been crying since yesterday. She started crying yesterday (start) and is still crying now (second point of time).
18. He worked on the farm for fifteen years before he retired. How long did he work for? Fifteen years.
19. I haven’t seen her since a long time ago. A long time ago is the starting point: a long time would be a duration of time.  
20. We’ve been waiting since noon. Noon is the starting point, now is the second point of time.