Present Unreal Conditional vs Future Real conditional

[Mrs9000]

Suppose I have a letter but haven't sent it yet.

If I send the letter Mary will not be happy. - Future real conditional

If I sent the letter, Mary would not be happy. - Present unreal conditional

What is the difference between the 2 sentences?
What is the context of the 2nd sentence? In the 2nd sentence, I didn't send this letter because it is an imaginary situation. In the 1st situation, I also didn't send the letter yet, so do both mean express the same information.

Please help!!!

[Alan]

Hi Mrs 9000,

I think you have answered your own question.

If I send the letter, Mary will not be happy - this is called a possible condition because it can happen

If I sent the letter, Mary would not be happy - this is called a probable or imaginary condition because it is something you imagine happening

Conditions or 'if' situations vary from a possibility to an impossibility and in the middle we have the imaginary one.

The impossible condition is purely theoretical because it's too late to do anything about it and following your examples it is:

If I had sent Mary the letter, Mary would not have been happy.

Alan
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English as a Second Language
You can read my ESL story Present Simple

[Mrs9000]

Hi Alan,

Thanks very much for your reply.
However, suppose I send the letter and in the letter that I wrote, I want to express the link between Mary being happy and me not sending the letter. In the letter would I say,

If I had not sent the letter Mary would have been happy.
or
If I didn't send the letter, Mary would be happy.

During the moment of my writing the letter I want to express the above idea.

A little confused.

[Fadihalloun]

by the way, what is the difference between:

If he arrives, we will go

&

If he arrives now, we go?

[Alan]

Hi Mrs 9000,

Changing the first part to negative changes the meaning but not the construction.

Alan.
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English as a Foreign Language
You can read my EFL story Progressive Forms