I am learning from this page
FORM 1 (Most Common Form)
[If ... Simple Past ..., ... would + verb ...]
If I want to use an "adjective"; say "busy". Is this sentence OK - actually I feel not:
If I was not busy tomorrow, I would come with you.
By the way, I'm not confined to Form 1. If in this case, another form must be used; it is OK.
Notice that that page says the future unreal conditional looks the same as the present unreal conditional. On, that page there is the note
EXCEPTION If I were ...
In the Present Unreal Conditional, the form "was" is not considered grammatically correct. In written English or in testing situations, you should always use "were." However, in everyday conversation, "was" is often used.
Examples:
If he were French, he would live in Paris.
If she were rich, she would buy a yacht.
I would play basketball if I were taller.
I would buy that computer if it were cheaper.
I would buy that computer if it was cheaper. Not Correct (But often said in conversation.)
I would not go so far as to call the use of was here incorrect; I would call it informal.
So, to be formal, and on a test, use
If I were not busy tomorrow, I would come with you.
To be informal, you can absolutely say:
If I wasn't busy tomorrow, I'd come with you.
Notice that in informal, everyday conversation, native speakers are also going to use those verbs contractions.
So realize that you will hear and read native speakers using was instead of were, and this is considered informal. The only people who consider it wrong all the time are called pedants (or learners who learn the rule and then say it must be used all the time).
The only time If I was sounds so bad that it is considered substandard is
?? If I was you,....
but even this is used by some native speakers, as part of their normal speech. I would definitely avoid using this on an examination. As a learner, if you say If I was you,... you will not sound natural and people may wince.
https://prezi.com/dlckl9y53yqh/present-and-future-unreal-conditionals/
I found this cool Prezi on present and future unreal conditionals. I knew somewhere I'd find the rule to use "were" regardless of subject...hope it helps.
It is not the case of any unreal conditional. It's a usual case of the Future Conditional (or, Conditional One). So, the grammatically and semantically right grammar structure for the idea behind your question is that: If am not busy tomorrow, I will come with you. The reason is that there is no unreal event in the - if clause. This event is really possible.
The second conditional can describe an unreal situation with reference to the present (-if clause). We imagine a hypothetical situation which contrasts with reality (the main clause). Then the semantics of your sentence must be transformed.
The real situation that you know in the present is that you are busy tomorrow. So, an unreal situation in the case is that you are free tomorrow.
So, you can desribe this unreal situation in an -if clause as follows: If I were free tomorrow. So, the whole sentence must be as follows:
If I were free tomorrow, I would come with you.
This problem is caused by a misunderstanding. The following syntax [If ... Simple Past ..., ... would + verb ...] is not correct. The correct syntax would be: [If ... Subjunctive ..., ... would + verb ...]
The subjunctive is the same as the past simple for all verbs except for "to be", where the past simple deviates from the rules (different 1st and 3rd person). Subjunctive of "to be" is formed the same way as all other verbs: all persons use the same word: "were".
