A long time ago I received the following e-mail regarding my "creative" use of the English grammar. It did not help much, my English tends to be creative still, but I think it is a super cute email :-)
You've sort of got the idea about 'will' and 'going to'. I think you've got it the other way round though.. The general difference in meaning between the two is that 'going to' is more certain than 'will'. You can actually use 'probably' with 'will' and 'going to'. I'll explain later.
In English we usually use future tenses in two ways: to make predictions and to express our intentions for the future.
We usually use 'going to' for predictions based on evidence. If there is evidence for a prediction then logically this makes it more likely it's going to come true than if there's no evidence at all.
Example 1: " Oh no, she's going to spank me".
I feel fairly sure about this prediction because there is some evidence for it: She's glaring at me. She's just taken her hairbrush out.
Example 2: "She`s definitely going to spank me".
Evidence: She's now yanked my pants down. I'm over her knees. My pale white bum is trembling like a blancmange as it waits for the first twack. There seems no doubt now that this spanking is going to take place. :-(
We use 'will' in predictions if we cannot be certain what we predict will take place.
Example. "She won't spank me tomorrow".
I feel fairly certain that this won't happen. She's just spanked me. My bottom is smarting. My eyes are full of tears. I intend to be a good boy from now on. She couldn't spank me twice in two days. Or could she ? In the end I have no sure way of knowing. Ultimately the fate of my bottom is up to her. If she decides to she wants to spank me again, then she will. What will be, will be. It's not my bottom.
Use 'going to' if you want to express an intention you've had for a long time: i.e. it is a plan.
Example: " I am going to give you the spanking of your life later".
I know when she says this she's been planning this for a while. I know there's going to be no way out of it. She's arranged to take some time out from her busy schedule to put me over her knees. (So nice of her, don't you think?). She's even bought a new hair brush. Later on, after she's spanked me, she's going to send me to bed for an early night without any dinner. She's arranged to go out with her friends.
Use 'will' when making a spontaneous decision.
Example: " I will spank you so hard you'll be screaming like a baby".
She's has just spontaneously come out with this decision. It's probably a response to something I've just done. Whatever the circumstances, things aren't looking too good for me.
'Probably', as I'm sure you already know, means something is approximately 75%-95% likely to happen. If she tells me "She's probably going to spank me" that's slightly better news than her telling me 'She's going to spank me',
All the rules as laid out above still apply when using 'probably'. Compare the two examples:
Example 1 " I am going to spank you".
Example 2 " I am probably going to spank you".
Both these statements express a plan she has (i.e they are expressing a plan she has. She has taken time out of her busy schedule etc...) However, in Example 2, although she's has made plans to spank me, she also acknowledges that there is a slight chance she might change her plans later.
The same logic applies to the use of 'will'. Compare the examples below:
Example 1 : " She won't spank me tomorrow"
Example 2" She probably won't spank me tomorrow".
In both these examples I'm making a prediction about the future. I recognise when I'm making these statements that I can't be entirely sure they'll come true. ( Note: I would be a lot better off if Example 1 is true. Example 2 may be true and yet I still might end up with a red bottom).
These are the general rules for using the simple future, but even though these are the general rules, many native speakers often break them. A lot of times in everyday English 'going to' and 'will' are used interchangeably."