for to mean ‘because’

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.

Here are some useful expressions using for

• I enclose a cheque/check for 100 euros
• What’s another word for stupid?
• I’ve known him for ages.
• I am all for making this change.
• Get ready.  -What for?   -Anne is coming.