We can use for to mean ‘because’. We only use this in very formal English.
- The divers have to be careful for a sudden change in conditions could be dangerous.
- Read the instructions carefully for you will only get one chance to enter the information.
We can use for to talk about a purpose or a reason.
- What did you that for?
- What is that for?
- Thank you for your letter.
- I don’t have enough money for the ticket.
- I need treatment for my bad back.
For can mean that you are in favour/favor of something.
- He is for the idea of cutting taxes.
- I am for this change in the way we do things.
- You need to stand up for what is right.
We can use for with expressions of time and distance.
- I walked for miles.
- I waited for a long time.
- We will be away for the next week.
Sometimes we can omit the for completely in these expressions without changing the meaning.
- I walked miles.
- I waited a long time.
With the present perfect, for refers to a length of time. Since refers to the starting point.
- I have studied English for seven years.
- I have studied English since I was 12.
