reason
The reason for something is the fact or situation which explains why it happens, exists, or is done.
I asked the reason for the decision.
The reason for this relationship is clear.
Be careful
Don't use any preposition except for after reason in sentences like these.
Don't use any preposition except for after reason in sentences like these.
You can talk about a person's reason for doing something.
One of his reasons for coming to England was to make money.
You can also talk about the reason why something happens or is done.
There are several reasons why we can't do that.
However, if you are actually stating the reason, don't use ‘why’. Instead you use a that-clause.
The reason that they liked the restaurant was its relaxed atmosphere.
The reason I'm calling you is that I know Larry talked with you earlier.
Note that the second clause in these sentences is also a that-clause. Instead of a that-clause, some speakers use a clause beginning with because.
The reason they are not like other boys is because they have been brought up differently.
This use of because is fairly common in spoken and informal English. However, some people think that it is incorrect, and you should avoid it in formal English.