What does "over a period of time" mean?
Not all past events happen in a single moment. Some things take time — they start at one point, continue for a while, and eventually end. A career lasts decades. A project takes months. A journey takes hours. A meeting takes minutes. All of these have a beginning and an end — and both the beginning and the end are in the past.
This is the situation we are dealing with here: an action or situation that stretched across a period of time in the past. The entire period — from start to finish — is now over and behind us.
Think of it like a closed tunnel. You entered at one end (the start), travelled through it (the duration), and came out the other end (the finish). The tunnel is entirely in the past. Nothing about it continues into the present.
The key ingredient: a duration expression
The clearest signal that we are talking about an action over a period of time is a duration expression — a phrase that tells us how long something lasted. These expressions almost always appear in this type of sentence.
from [time] to [time] → from 1990 to 2005
throughout + period → throughout the 1980s
during + period → during his time at the company
The most important of these is for. When you see for + a period of time in a past sentence, the Past Simple is almost always correct — provided the period is now finished.
How is the Past Simple formed?
The form is identical to all other uses of the Past Simple. The tense itself does not change — only the meaning changes depending on context.
Affirmative sentences
She worked there for fifteen years. · He studied Japanese for four years.
They ran the business from 2005 to 2015.
- She worked at the hospital for fifteen years before she retired.
- My family lived in Canada for five years before moving back to Europe.
- He studied architecture for six years before switching to engineering.
- They ran the business together for over a decade before selling it.
- The war lasted for four years and caused enormous suffering.
Negative sentences
She didn't work there for fifteen years — only for five.
They didn't run the business together — one partner left early.
- She didn't work at the hospital for fifteen years — only for five.
- My family didn't live in Canada — they lived in Australia.
- He didn't study architecture — he studied civil engineering.
- We didn't wait three weeks — we only waited three days.
- The conflict didn't last four years — it ended in six months.
Interrogative sentences (questions)
Did she work there for fifteen years?
How long questions: How long + did + subject + base verb + ?
How long did she work there? · How long did the war last?
- How long did she work at the hospital?
- How long did your family live in Canada?
- How long did they run the business together?
- Did he study architecture for six years?
- How long did the war last?
The logic of time — why not the Present Perfect?
This is one of the most common areas of confusion for ESL learners. Both the Past Simple and the Present Perfect can be used with for — but the key difference is whether the period is finished or still connected to now.
Present Perfect + for = the period continues into the present → She has worked there for fifteen years. (She still works there now.)
The test: Is the action still happening? If yes → Present Perfect. If no → Past Simple.
Common time expressions for this use
Common mistakes to watch out for
✗ She has worked there for fifteen years before she retired.
✓ She worked there for fifteen years before she retired.
The phrase 'before she retired' tells us this period is over — she is no longer working there. The Present Perfect cannot be used with a closed past period. If the story is finished, use the Past Simple.
✗ She was working at the hospital for fifteen years before she retired.
✓ She worked at the hospital for fifteen years before she retired.
The Past Continuous describes an action in progress at a specific moment — not a duration. When you say something lasted for a period of time and that period is now over, always use the Past Simple. Think: completed duration = Past Simple.
✗ She worked there since fifteen years.
✓ She worked there for fifteen years.
✓ She has worked there since 2010. (if she still works there)
For is followed by a duration (an amount of time): for five years, for a long time, for decades. Since is followed by a point in time (when it started): since 2010, since Monday, since she was a child. Also note: since is almost always used with the Present Perfect, not the Past Simple.
✗ She works at the hospital for fifteen years before she retired.
✓ She worked at the hospital for fifteen years before she retired.
The phrase 'before she retired' clearly places the whole situation in the past. Both verbs must be in the past. Always check that every verb in a past time context is in the correct past form.