For, since and ago: three ways to talk about time
How long, since when, and how long back — three small words that learners swap more than any others.
Three small words, each answering a different question. They are easy to confuse, because many languages express all three with roughly the same phrasing.
Which answers what
| Word | Question | Example |
|---|---|---|
for | how long? | for two years |
since | starting when? | since 2019 |
ago | how far back? | two years ago |
The whole difference is there: for is the length of a stretch, since is its beginning, ago is a point in the past.
The test
Ask what follows the word:
- A stretch (
two hours,a week,ten years) →for - A point (
Monday,2019,I was a child) →since
for three days and since Monday can describe the same time, named two ways.
ago comes after, not before
It is the only one of the three that follows its phrase:
- two years ago ✓
- ago two years ✗
And it always takes the Past Simple, never the perfect:
- I saw him two years ago. ✓
- I have seen him two years ago. ✗
The reason is simple: ago names a finished point in the past, and the perfect refuses finished points.
Where for and since live
Both usually arrive with the Present Perfect, because they describe something that started earlier and is still going:
- I have lived here for ten years. — and I still do.
- I have known her since 2019. — and I still do.
This is where most learners slip: their own language uses a present tense here — "I live here ten years" — and the hand reaches for I live here for ten years. It is wrong, and it is audible.
Three sentences worth memorising whole
Not as a rule, just as they are:
- How long have you been here?
- I've been here for an hour.
- I've been here since three.
Those three lines cover nearly every everyday case.
for does other work too
for also means "intended for": This is for you. One word, two jobs, never confusing in context.
since has a second meaning as well — "because": Since you're here, let's start. Rarer, but it appears.
Where this sits in the course
In Lymi for, since and ago are lesson nineteen, and the placement is deliberate: four Present Perfect lessons come before it, and lesson twenty follows immediately, putting the perfect and the simple past side by side so you have to choose. By then it is clear why ago pulls one tense and since pulls another.