For and Since
Both of these are used to indicate a time span. In other words, if you are answering the question “How long ~?”, you want to use “for” or “since.”
“For” is used when you are using a specific period of time: one week, three hours, five years, etc.
I have been working on my homework for two hours.
Father has been sick for a week.
Tom has been attending college for three years.
She’s been waiting for the bus for a long time.
“Since” is used when you indicate the beginning of a specified period of time. The period of time continues until the present.
I have been working on my homework since 1 o’clock.
Father has been sick since Sunday.
Tom has been attending college since 2005.
She’s been waiting for the bus since this morning.
“Ago,” on the other hand, just refers to some time in the past. “Ago” uses the simple past tense. You can think of “ago” = “before now.”
I worked on my homework four days ago. (= “I worked on my homework four days before now.”)
John came home from college a month ago. (= “John came home from college one month before now.”)
People lived in caves a long time ago.
Exercise: Complete the following sentences, using “for” or “since.”
I have been practicing the piano ____________ 3 o’clock. ==> I have been practicing the piano since 3 o’clock.
I have been practicing the piano ____________ 90 minutes. ==> I have been practicing the piano for 90 minutes.
1. Jane has been absent from class ____________ Monday.
2. Jane has been absent from class ____________ several days.
3. The baby has been walking ____________ two months.
4. The baby has been walking ____________ January.
5. We have been in business ____________ 2001.
6. We have been in business ____________ over five years.
7. She’s had a pet monkey ____________ last year.
8. She’s had a pet monkey ____________ months.
9. Keith has been playing the piano ____________ he was a young child.
10. Keith has been playing the piano ____________ 20 years.
Exercise: Complete the sentences, using the word in the parentheses and “for” or “ago.”
I went on vacation (three weeks). ==> I went on vacation three weeks ago.
I have been on vacation (a week). ==> I have been on vacation for a week.
1. We have been driving (six hours).
2. We drove to California (two months).
3. Sam went to the library (ten minutes).
4. Sam has been at the library (three hours).
5. Jim lived in Hawaii (many years).
6. Jim has lived in Hawaii (sixty years).
7. The kids played outside (45 minutes).
8. The kids played outside (two days).