I am often confused with the usage of since and from.
I know him from 15 years
I know him since 15 years.
Which one is correct? How would I decide which is the right preposition to use?
'Since' talks about one particular point of time till now.
I have been working since 7 am
'From' in most of the cases talks about the starting point and ending point. Said that, the format could be 'from....to/till/until'
The shop is open from 9 in the morning to 6 in the evening
Quite close is 'since' and 'for'
Okay, as I said, 'since' talks about a particular point. So, you need to mention "since" which date the thing has been happening.
On the other hand, 'for' is used for a total period of time and you don't need to define a starting point.
The best example I can think of is...
I have been waiting for two hours
I have been waiting since 2 o'clock
In the latter example, you need to define the starting point.
I have been living in this house for 10 years
I have been living in this house since 2005
So, in your case, you have known him for the past 15 years OR since 2000.
When we use 'since' we generally refer to a particular point of time or a specified time in the past. For example - He has been living here since 1988. She has been awake since dawn / 5'o clock. They have been working here since their youth. So the sentence - " I know him since 15 years " - is wrong. The correct form is - " I know him for 15 years ".
In the same way ' from ' is also used to refer to a particular point of time, and in addition to it, it can also be used to refer to the starting point as well as the ending point. For example - The world cup will start from 14th February. We lived in Oslo from 1988 to 2009.
To refer to a period of time we generally use 'for'. For example - It has been raining in New York for three days.