[Grammar in Use Unit 12] For, Since and When and How long

Posted: 7/9/2026 • Study Notes

Following the previous post, we will take a deeper look at for and since, which are inseparable from the present perfect tense.

In this Unit 12, we will spend time looking at for and since in more detail, and also summarize the difference between When and How long, which require a complete change in tense when asking questions.

1. Review of For and Since

These are used when you want to say 'how long' an event has been happening, and the nature of the noun that follows them is different.

for + a period of time: Used to say how long something has lasted.
- Sally has been working here for six months.
- I haven’t seen Tom for ages.
since + the start of a period: Used to say exactly when something began.
- Sally has been working here since April.
- I haven’t seen Tom since Monday.

2. Three Rules for For

① Omissible in affirmative sentences, mandatory in negative sentences

In affirmative (positive) sentences, the meaning remains clear even if you omit for, but in negative sentences, you must keep it.

They’ve been married for ten years. = They’ve been married ten years. (Omission possible)
They haven’t had a holiday for ten years. (for is mandatory)

② `in` can be used instead of `for` in negative sentences

Exclusively in negative sentences, in can be used with the exact same meaning as for.

They haven’t had a holiday in ten years. (= for ten years)

③ Do not use `for` before `all...`

Never use for before expressions like all day or all my life.

⭕ I’ve lived here all my life.
❌ I've lived here for all my life.

3. When + past tense vs. How long + present perfect

The tense of the entire sentence changes depending on the first word you use to start the question. This is a part where I personally make a lot of mistakes.

When...? ➔ Past tense only! (Because you are only interested in 'a point in the past' when the event occurred)
How long...? ➔ Present perfect only! (Because you are interested in the 'duration' that has continued from the past until now)

When it's raining

When did it start raining?
- It started raining an hour ago / at 1 o’clock.
How long has it been raining?
- It’s been raining for an hour / since 1 o’clock.

Knowing each other

When did Joe and Kate first meet?
- They first met a long time ago.
How long have they known each other?
- They’ve known each other for a long time.

4. Useful patterns to know: It is / It has been ~ since...

This is a very convenient structure to use when you want to say something like, "It's already been two years since I last did ~." Both It is and It's been can be used interchangeably.

"It’s two years since I last saw Joe." = "It’s been two years since..."
- (It has been two years since I last saw Joe. ➔ Meaning I haven't seen Joe for two years.)
"It’s ages since we went to the cinema." = "It’s been ages since..."
- (It's been a long time since we went to the cinema. ➔ Meaning we haven't been to the cinema in a long time.)
"How long is it since Mrs Hill died?" = "How long has it been since..."
- (How long has it been since Mrs. Hill passed away? ➔ Meaning when did she pass away?)

Closing

Let's review until the past tense (did) reflexively pops up after When, and the present perfect (have p.p.) appears after How long.
If you memorize the It's [time] since [past action] pattern, you can naturally say, "It's been a long time since I..."

This concludes the summary of Unit 12.

In the next post, we will take some time to review part of what we have learned by creating example sentences, just like last time.

Let's all study step-by-step, little by little, and consistently together.

Keep up the good work today!