Albate I think this issue is pertaining to the standard or slang English, Still I want to ensure if it's related to that or not.
Since I came across many times in movies and some everyday english talks they use the main clause of the 3rd conditional as the next part of a wish clause. The following example could illustrate much easier though.
i. I wish I could've gone there.
ii. I wish I had gone there.
Regarding the example, I need to know:
1.What's the difference between two in terms of meaning?
2.Is this variation regarded to the issue of standard/slang English or they totally differ from each other in terms of grammar?
Best Answer
Both are normal grammatical English, not slang.
A key difference is that "could have" often emphasizes a passive lack of opportunity, while "had" sometimes implies an active decision.
I could not. Why not? For unstated reasons: it was not possible, I could not have gone, I wish the universe had been otherwise, I wish I could have gone.
I did not go. Why not? Perhaps due to an unstated choice: I chose not to go, I wish that I personally had made a different choice, I wish I had gone.
Note that "had gone" does not unambiguously claim choice and responsibility -- however "could have gone" clearly denies choice and responsibility.