1. WHEN DO WE USE WILL? WHEN DO WE USE BE GOING TO?
BE GOING TO AND WILL
WHEN DO WE USE WILL?
WHEN DO WE USE BE GOING TO?

2. We use WILL and WON’T…
To make general predictions about the future. We often use THINK, HOPE, EXPECT, IMAGINE, etc. with WILL and WON’T to express our opinion about the future.
-I don’t think Donald Trump will win the election.
When we decide to do something at the moment of speaking, for example when we suddenly offer to do something for someone.
-María: It’s hot in here!
-Miguel: I’ll open the window.
To talk about the future when we consider it to be an objective truth.
-Greenpeace began in In 2021 it will celebrate its 50th anniversary.
DEFINITELY, PROBABLY, PERHAPS, IT’S POSSIBLE THAT, MAY (MAY NOT), MIGHT (MIGHT NOT, MIGHTN’T) are used with WILL to say how certain we think something is.
When we are very certain we use…
When we are quite certain we use…
When we are 50% certain we use…

3. We use be going to…
To talk about plans and intentions for the future. We use it for things that we have already decided to do in the future.
-We’ve decided that we’re going to join the WWF.
To make predictions about the future, particularly when we have EVIDENCE for the prediction.
-That car is going very fast. I think it’s going to crash.

4. Look at the position of the adverbs DEFINITELY and PROBABLY…
This will probably affect plants and animals.
Global warming will definitely make a big difference.
The changes probably won’t be immediate.
Things definitely won’t get better until we do something.
WHAT DO YOU NOTICE?

5. In a nutshell…
The key difference between WILL and BE GOING TO is that if you make a decision at the moment you speak, you use WILL:
-María: Do you want to go to the cinema tonight?
-Miguel: Sure, I’ll see you there at 8pm.
SHALL can be used as an alternative to WILL, but it is much less common. The contracted forms of SHALL NOT and WILL NOT are SHAN’T and WON’T. They are both used to make predictions about what will happen in the future:
-We shan’t be there before 5 pm.
-I won’t see Sarah at the party.
SHALL and SHAN’T are used ONLY with first person pronouns (I and WE).