The phrase in the title is obviously incorrect; however, I’m having difficulties figuring out how it could actually be grammatically constructed. To be clear, I’m aware this is a ridiculous construction, but given that such a tense could theoretically (as far as I’m aware) be combined with the word “lest”, I feel that there has to be some technically correct construction.

Here’s what I know so far:

“Lest” is an unusual word in English. Wikipedia tells me it’s in the subjunctive mood, and requires the use of the following verb in its bare form (the infinitive minus “to”). While this makes sense for basic sentences, I’m not convinced that it’s sufficient for constructing sentences where the first clause has a complicated verb tense.

Here are some example sentences I’ve been thinking about; I’m not sure how many of these are correct, but I’ve tried to do what seems best:

1. “I run, lest they catch me.”
2. “I will run, lest they catch me.”
3. “I must run, lest they catch me.”
4. “I ran, lest they should catch me.”
5. “I had run, lest they should have caught me.”
6. “I have been running, lest they should catch me.”
7. “I had been running, lest they should have caught me.”
8. “I should have been running, lest they catch me.”
9. “I should have run, lest they might have caught me.”
10. “I should have been running, lest they might have caught me.”
11. “I must have been running, lest they should have caught me.”
12. “I will have been running, lest they have been catching me.” Or perhaps more likely: “I will have been running, lest they should catch me.”

One difficulty I see is that some sentences with the first clause in the past tense simply don’t seem to make sense with the second clause in the infinite. For instance:

7. “I had been running, lest they should have caught me.” vs.

7.1. “I had been running, lest they should catch me.”

To me it seems like 7 makes more sense than 7.1, but I can’t grammatically articulate why this would be the case (if it is), beyond the notion that using the bare infinitive in the second sentence confuses the order of events (e.g., running happened in the past, but “lest they should catch me” implies the catching hasn’t happened yet). Other example also seem to include temporal context, such as the differences between 4, 10, and 11.

11. “I must have been running, lest they should have caught me.” vs.

11.1 “I must have been running, lest they should catch me.”

Again, 11.1 seems not to make sense, as 11 implies some degree of uncertainty regarding the speaker’s prior actions. E.g.:

“How did you escape?”

“Well, I must have been running, lest they should have caught me.”

To wrap back around to the original question, I can imagine almost no scenario in which this would be used, but consider the following:

“By the time you get here, I will have been working on the project for
an hour, lest I have nothing to show you.”

In this case, the bare infinitive seems natural. Perhaps this means the correct form is indeed, “I will have been running, lest they catch me.”

That said, I still have questions about the other examples above, particularly 4 through 11.

Specifically:

• Which of these, if any, are correct?
• What would be the grammatically correct ways of formatting these sentences?
• Is there a grammatical rule that can be used to understand the use of the word “lest” in any possible context? (Whenever I look this up, I can only find people providing example sentences, never an actual rule.)

If anyone has any insight to offer, I would be very appreciative. Please let me know if there are any clarifications I should add, lest I unduly confuse anyone. 🙂