Mixed conditionals (future-past)

[Fanchette]

Hi,

In 'Grammar in context' by Hugh Gethin I found the information: 'Sometimes the conditional or past tense is 'shifted back' to the conditional perfect or past perfect to give a sentence with uniform tense use:

I would have come with you tomorrow if I hadn't already promised...
I would have accepted your invitation if I hadn't been going out tomorrow.

So, my question is: when exactly can we use it? What is this 'sometimes'? :)
I really need the answer. Thank you in advance!

[5jj]

I do not understand Gethin's 'uniform tense use'.

In your two sentences. we understand the speaker to have in mind something like 'At the past time when you invited me, ...' The so-called third conditional, used of a past counterfactual situation, is appropriate.

[Tdol]

The speaker is using a third conditional, which normally talks about a past event, to talk about the future. The effect of this is to show that the reason why the person cannot come lies in the past.

[Fanchette]

Let me be sure I understand the explanation correctly.

The effect of this is to show that the reason why the person cannot come lies in the past.

In this case "if I hadn't been going out tomorrow" means something like "if I hadn't already arranged going out tomorrow"?

[5jj]

In this case "if I hadn't been going out tomorrow" means something like "if I hadn't already arranged going out tomorrow"?

Yes

[ostap77]

Would such conditionals sooner be used in literature than in conversation?

[5jj]

Would such conditionals sooner be used in literature than in conversation?

No

[Fanchette]

Thank you very much!