I was listening to a news report on the radio last night and heard a non-native speaker of English, make a very common grammar mistake, misusing the prepositions ‘for’ and ‘since.’ So, I thought today I would write a review of how to use these words correctly as prepositions when talking about time.

In English we use ‘for’ when we are talking about or measuring a duration of time, that is to say, when we say how long something lasts up to the present time. We most often use the present perfect tense with ‘for’ as in this example:

I have known how to speak English for a long time.

Here we are talking about something that started in the past and continues to the present.

When using the present tense with ‘for’ we are referring to a period of time that extends into the future, as in this example:

How long are you here for? (The question could also be ‘Until when will you be here?)

We can in fact use all verb tenses with the time preposition ‘for’, as long as we are talking about something that started in the past and continues to the present (even if it is just about to stop).

Examples:
They practice their English for 1 hour every day.
They are practicing for 2 hours today.
They have lived in America for a long time.
They have been living in America for 1 year.
They worked in America for 2 years.
They will be in America for at least 1 month.

One final note about ‘for’, don’t use the expressions ‘all day’ and ‘all the time’ with the preposition for.

Examples:
He was there all day. (Correct)
He was there for all day. (Incorrect)

In English we use the word ‘since’ to talk about the starting point of actions, events, or states of being. ‘Since’ is used to refer to when something began or started; the action may continue to the present, but it also may have stopped. ‘Since’ is always used with a specific time, date, or age (7:00pm, January, or 5-years-old, prehistoric time). ‘Since’ is generally used with the present perfect, past perfect, and past perfect continuous tenses. For example:

I’ve been studying English since 5 o’clock.
I have studied since 5 o’clock and I am tired.
I had been studying since 5 o’clock and I was getting tired.

‘Since’ is also often used in the following sentence construction: it has been + period of time + since.

For example:
It has been two months since I last spoke English.

Okay, now here is the summary, or take-away, from this review:

Use FOR to talk about a period (or duration) of time.
Use SINCE to talk about the starting point of a period of time (that continues, or went on for some time, but has now stopped).

Also remember that ‘for’ and ‘since’ do have other meanings in English that are not associated with time. For example:

This book is for you.
Since he didn’t study he didn’t pass the quiz.