Q: In one of her essays, a college professor has the following sentence: “I replied that I wouldn’t answer questions until I’d had time to consider the charges.” Why is the past perfect used after the word “until”? I believe the simple past would suffice.
A: We think the professor’s choice of words was appropriate.
Either the simple past tense (“not … until I had time”) or the past perfect tense (“not … until I had had time”) would be grammatically correct, though each creates a slightly different effect.
The use of the past perfect in the “until” clause emphasizes the need for time to consider before answering. The use of the simple past—“I would not answer … until I had time to consider”—plays down the before-ness and deemphasizes the amount of time needed to consider.
This is a subtle difference. But we found a good illustration of it in The Grammar of the English Tense System: A Comprehensive Analysis (2006).
The book, by Renaat Declerck in collaboration with Susan Reed and Bert Cappelle, uses a positive instead of a negative “until” construction, but the principle is the same. Here are the examples (the brackets are theirs):
(1) “[Bill said] he would stay in the pub until Jill arrived.” (The simple past “arrived” implies that Bill would stay “until the time of Jill’s arrival,” the authors say. The times of the “would” clause and the “until” clause are simultaneous.)
(2) “[Bill said] he would stay in the pub until Jill had arrived.” (The past perfect “had arrived” implies that Bill would stay “until such time as Jill had already arrived,” the authors say. The time of the “until” clause occurs before that of the “would” clause.)
Both versions are correct, but they have slightly different meanings. Negative versions, with “not … until,” might be expressed this way:
“[Bill said] he would not leave the pub until Jill arrived” … or … “until Jill had arrived.”
In another book, Conditionals: A Comprehensive Empirical Analysis (2001), Declerck and Reed write: “Not … until frequently introduces a time clause with a conditional connotation.”
One of their examples is “I won’t give you your bike back until you’ve paid me back the £20 I lent you last year.”
The speaker could have used the simple present tense in the “until” clause (“until you pay me”), but the use of the present perfect (“until you have paid me”) emphasizes the difference in time frames; they’re not simultaneous.
We might paraphrase this as “I intend to give the bike back, not when you pay me, but after you’ve paid me.” The difference in time frames emphasizes the condition that the speaker places on the action.
from Grammarphobia https://www.grammarphobia.com/blog/2017/06/not-until.html