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Hi, I'm Jennifer. And this week, we'll learn about the difference between FOR and SINCE. FOR and SINCE are always very difficult for my students. In fact, I hear students mistaking them almost every day. 

It's very simple, once you learn my trick. Let's get started.

What's the difference between FOR and SINCE? We use FOR and SINCE to answer the question "How long?" FOR can be used in the present, the past, and the future. I studied FOR 9 hours….past. We’ve been on holiday FOR 2 days.…present perfect. I’ll be in China for 4 weeks.…future.

We use FOR with a time interval... 

FOR 9 years, FOR 9 days, FOR 9 minutes. We can also use FOR when the time interval is not exact. FOR a while. FOR a long time. FOR a short time. FOR ages. I’ve known my best friend FOR years. She’s been studying FOR a really long time. He’ll be at the office FOR a while.

SINCE can only be used in the present perfect or the past perfect, not in the future. We use SINCE with a moment in time... 

like a year. She’s lived in Paris SINCE 1999…present perfect. I haven’t seen them SINCE Christmas…present perfect. We’ve been waiting SINCE 12:30…present perfect continuous.

We can use FOR and SINCE to express the same idea, but we use it in different ways. We’ve lived in Madrid FOR nine years. Time interval. We’ve lived in Madrid SINCE 2007. Moment in the past. It's the same idea, but we say it differently. Let's look at another example. I’ve been working FOR 6 hours. I’ve been working SINCE 6 o’clock.

We often use the word AGO when we are talking about the past. It means: A moment before now. We know that use FOR with time intervals, like twelve days. But, we can also use AGO. AGO is a moment in time, so we don't use FOR, we use SINCE. I’ve been studying SINCE 12 days ago. Any time interval that we can use FOR, we can also use AGO, but we must use it with SINCE, because it is a moment in the past.

Shall we practice?

How long do you think this woman has been running? Now remember, SINCE is a moment in time. Maybe she’s been running SINCE sunrise. Or SINCE 6:45 am? Or SINCE she woke up? How long has she been running FOR? Remember, FOR is a time interval. She’s been running FOR an hour. Or FOR 15 minutes. Or FOR a long time.

What about this family? They will go on vacation FOR 3 weeks. FOR a month. FOR the whole summer...if they're lucky. What about SINCE? They will go on vacation SINCE…..Ah! You caught me. I was trying to trick you! We can't use SINCE when we are talking about the future.

So remember my tip when deciding which to use, FOR or SINCE and visualize the word. FOR is used for time intervals and SINCE is used for moments in time.

I've been teaching English for many years, but ever SINCE I taught my students this trick, they've never made the mistake again.