Unreal uses of past tenses "if only+simple past" vs "if only+past perfect"

Question

If only I knew the answer!

What's the difference between simple past and past perfect in unreal uses of past tenses?

● What's the difference between these two sentences?

1. If only you didn't forget the map, we would be there by now.

2. If only you hadn't forgotten the map, we would be there by now.

I know that we use simple present to talk about things we would like to be different in the present/or future (but which are impossible or unlikely) and what we now want to achieve.

And we use past perfect to talk about things that happened/didn't happened in the past and that what we now regret.

● Are there any more differences between simple past and past perfect which I didn't mention?

● With these explanations, how can I answer questions like the following question?

● Should we recognize that the question is talking about a regret from the past, or a sensation that is about the present or the future?

A: Do you wish you ________to college or do you think you made the right decision to leave school and start working?

a) Went

b) had gone

c) would go

d) would rather go

(I think b sounds better because the questioner is asking about something that happened in the past)

And what about this:

B: It __ a difficult problem. I wish I _____ the answer to it!

a) is - had known

b) is - knew

c) was - had known

d) was - knew

(The best answer is b, I suppose. In this case it's about an impossible imagination, but I wonder whether it's in the present or not.)

C: He should be less stingy! Then he'd enjoy life more.IF ONLY

___________________________________, he'd enjoy life more.

a) If only he were less stingy

b) If only he had been less stingy

& Can we use if only... instead of wish with the simple past and past perfect? For example:

X:

I wish I hadn't spoken to Emma like that - you know how sensitive she is.

Y:

(a)If only I hadn't spoken to Emma like that - you know how sensitive she is.

(b)If only I hadn't spoken to Emma like that, she would be here by now.

Answer 1

To my AmE ear

If only you didn't forget it. ^NO

is ungrammatical as a wish that something had not taken place. The grammatical version is:

If only you had not forgotten it. ^YES

Your I wish | If only examples with Emma are all grammatical.

With respect to the college example:

Do you wish you had gone to college?

is grammatical and

Do you wish you went to college?

is spoken by a fairly large fraction of speakers of AmE, most of whom probably did not go to college.

P.S. Mv Log asks in a comment: "What about If only you didn't forget the map every time we set out, we would be there by now?"

In the original question, the context is a single past action the speaker is ruing, speaking to Emma in a particular manner. She (presumably Emma) would be there by now if those words hadn't not been spoken as they had been spoken. The backshift is from past spoke to past perfect had spoken to indicate the Past Non-Actual:

If only I hadn't spoken to Emma like that...

In Mv Log's query, the phrase every time changes the aspect from a rueful wish about a single past incident (spoke in the Emma example or forgot in the map example) to a wish concerning what always happens. We use the simple present to refer to the general state of things or to things which always happen, and thus the backshift is from present forget or do forget to simple past; the negated simple past uses did: did not forget

You always forget the map. If only you did not forget it all the time!

Of course we could also use modal would:

... If only you would not forget it all the time!