How to invert if-clause in continuous form?

Question

I want to know how to invert these if-clauses in conditionals (for the convenience, I'd leave the main-clause):

• If I am not going to catch the train... (a real conditional)

• If I were not going to catch the train... (an unreal conditional in the present)

• If had not been going to catch the train... (an unreal conditional in the past)

It doesn't matter whether the second and the third don't make sense. I just want to know how to invert them. I've written my attempts below, please correct me if there's any mistake. Thank you.

• Should I not be going to catch the train...

• Were I not to be going to catch the train...

• Had I not been going to catch the train...

Anyway, the reason I'm asking this question is my confusion about the infinitive-to after were I not. I don't know whether to is necessary there.

Thanks in advance.

Answer 1

"Should" conditionals refer to an uncertain situation. The most common usage is with a following imperative:

• Should you run into difficulties, don't hesitate to contact me.

But in formal English, they can also substitute for the "if I"+present tense structure:

• Should I miss the train, I shall catch the bus.

However, I don't think you can use "should" to refer a present where you already know the answer, or to a recurring event:

• (?) Every day, should I miss the train, I catch the bus.
• (?) Should I not be on the train right now, where do you suppose I am?

"Should" seems to sit uncomfortably with continuous tenses. "Should I not be going to catch the train..." is technically correct, but it isn't obvious where or when it would be appropriate to use it.

Were "If I weren't going to catch the train" can be inverted to "Were I not going to catch the train".

You have suggested "Were I not to be going to catch the train", which would instead be the inversion of "If I weren't to be going to catch the train", a more awkward construction.

Had "Had I not been going to catch the train" is absolutely fine.