Going To

Going to
Going to is not a tense. It is a special expression to talk about the future.
Structure of Going to
The structure is:
Subject + be + going + infinitive
The verb be is conjugated (past, present or future).
  | subject | be | (not) | going | infinitive |   |
+ | I | am |   | going | to buy | a new car. |
+ | I'm |   | going | to go | swimming. |
- | He | is | not | going | totake | the exam. |
- | It | isn't | going | to rain. |   |
? | Are | you |   | going | to paint | the house? |
Use of Going to
Going to - intention
We use going to when we have the intention to do something before we speak. We have already made a decision before speaking. Look at these examples:
* Jo has won the lottery. He says he's going to buy a Porsche.
* We're not going topaint our bedroom tomorrow.
* When are you going to go on holiday?
In these examples, we had an intention or plan before speaking. The decision was made before speaking.
Going to - prediction
We often use “going to” to make a prediction about the future. Our prediction is based on present evidence. We are saying what we think will happen. Here are some examples:
* The sky is very black.It's going to snow.
* It's 8.30! You're going to miss the train!
* I crashed the company car. My boss isn't going to be very happy!
In these examples, the present situation (black sky, the time, damaged car) gives us a good idea of what is going to happen.

Will
One of the most common ways to talk about the future is with will, for example: I will call you tonight. We often call this the"future simple tense", but technically there are no future tenses in English. In this construction, the word will is a modal auxiliary verb.
Here are the three main ways that we use will to talk about the future.
No plan
We use will when there is no prior plan or decision to do something before we speak. We make the decision at the time of speaking. Look at these examples:
* Hold on. I'llget a pen.
* We will see what we can do to help you.
* Maybe we'll stay in and watch television tonight.
In these examples, we had no firm plan before speaking. The decision was made at the time of speaking.
We often use will with the verb think:
* I think I'll go to the gym tomorrow.
* I think I'll have a holiday next year.
* I don't think I'll buy that car.
Prediction
Weoften use will to make a prediction about the future. Again, there is no firm plan. We are saying what we think will happen. Here are some examples:
* It will rain tomorrow.
* People won't go to Jupiter before the 22nd century.
* Who do you think will get the job?
Be
The verb be is an exception with will. Even when we have a very firm plan, and we are not speaking spontaneously, wecan use will with be. Look at these examples:
* I will be in London tomorrow.
* There will be 50 people at the party.
* The meeting will be at 9.30 am.
May
We can use 'may' to ask for permission. However this is rather formal and not used very often in modern spoken English
* May I borrow your pen?
* May we think about it?
* May I go now?
We use 'may' to suggest somethingis possible
* It may rain later today.
* I may not have time to do it today.
* Pete may come with us
Might
We use 'might' to suggest a small possibility of something. Often we read that 'might' suggests a smaller possibility that 'may', there is in fact little difference and 'might is more usual than 'may' in spoken English.
* She might be at home by now but it's not sure at all.* It might rain this afternoon.
* I might not have time to go to the shops for you.
* I might not go.
For the past, we use 'might have'.
* He might have tried to call while I was out.
* I might have dropped it in the street.
Must (subjective obligation)
We often use must to say that something is essential or necessary, for example:
* I must go.
Structure of Must...