What is the tense of "wasn't interrupted"

Question

So I'm writing a book and English is not my native language. As I've gotten deeper into the writing process I noticed that I'm almost randomly choosing between past tenses without making much logic (which I realized 20 pages into the book). Therefore, I started relearning all the English tenses in an attempt to proofread what I've written so far on my own. Long story short, there is one sentence in which I just can't put a finger on a specific tense.

"If this day wasn't interrupted by a sudden radio cast, so and so would have happened." (the so and so is not relevant)

I'm thinking past perfect simple, but I can't see any reasoning behind it; it just sounds fitting. My problem is there is no "had". Would that sentence make any more sense if I exchanged "wasn't" with "hadn't been"?

Thanks a bunch!

Answer 1

Both these sentences are well-formed grammatically, but they are not used for the same thing:

1. He wasn't thinking straight.
   FEATURES: past tense, continuous aspect
2. He hadn't been thinking straight.
   FEATURES: past tense, perfective aspect, continuous aspect

Both sentences’ verbs are in the past tense (was, had), and both sentences are also marked with the continuous/progressive aspect. However, only the second is marked with the perfective aspect used to indicate a completed action.

In English, the perfect aspect is most commonly indicated with a past participle like had spoken, has spoken, will have spoken, but can also be indicated by using do in the past tense as in did speak. An otherwise unmarked past tense like spoke can and usually does indicate a completed action, but not always.

Sentence 1 in unmarked by any perfective aspect, so it can be understood to have imperfect aspect, meaning that it is incomplete or ongoing. Imperfects are also used in narrative pasts, where they can be combined with clauses using perfects to used to help order events.

English doesn’t have a dedicated imperfect form of the verb the way some langauges have, so we typically employ other markers to clarify this, most commonly a form of be and the continuous aspect. Here the continuous aspect marks the first clause as ongoing to better place the second clause’s completed actions as “punctuating” or interrupting the first clause’s narrative state:

3. I was still thinking about what to do for supper when the pizza-delivery guy appeared and told me that this one was on the house.

Now let’s look at your original pair of formulations:

4. If this day wasn't interrupted by a sudden radio cast, so-and-so would have happened.
5. If this day hadn't been interrupted by a sudden radio cast, so-and-so would have happened.

The second clause in sentence 4 and 5 is the same: so-and-so would have happened. That’s the modal auxiliary would combined with a (bare) “perfect infinitive”. The perfect aspect used for have happened means that it’s talking about a completed action. The modal would can be used to mean a surprisingly wide variety of things, but when combined with a perfective like it is here with have happened, virtually always indicates an unreal past, one that did not occur.

Almost always when you have a conditional’s consequent of this particular variety, the conditional’s antecedent uses a past tense. (If you prefer Greek terminology over Latin, you can say apodosis for the consequent and protasis for the antecedent.) However, the other aspects can vary depending on quite a bit depending on intended meaning.

Here you’ve used a passive construction in the antecedent clause, which complicated matters a tiny bit because it drags the verb be plus past participle into the picture. This is perfectly fine of course, but just to simplify talking about it let me temporaily uninvert subject and object to recast that part into an active clause with a direct object again.

6. If a sudden radio cast didn’t interrupt this day, so-and-so would have happened.
7. If a sudden radio cast hadn’t interrupted this day, so-and-so would have happened

If you flip it from a negative to a positive for illustration purposes, now you can skip the do support:

8. If a sudden radio cast interrupted this day, so-and-so would have happened.
9. If a sudden radio cast had interrupted this day, so-and-so would have happened,

Both versions are grammatical. The antecedent is in the past tense in both 8 and 9, but only 9 uses the perfect aspect there. A very great many English conditional statements start out with a plain past tense and no other aspects the way we see in sentence 8. Here for example are a few such possibilities, all perfectly grammatical but meaning different things:

10. If a radio cast interrupted the day, everything stopped.
11. If a radio cast interrupted the day, everything would stop.
12. If a radio cast interrupted the day, everything will have stopped.
13. If a radio cast interrupted the day, everything would have stopped.

If you switch those back to passives in the antecedents, you get:

14. If the day was not interrupted by a radio cast, nothing interesting happened.
15. If the day was not interrupted by a radio cast, nothing interesting would happen.
16. If the day was not interrupted by a radio cast, nothing interesting will have happened.
17. If the day was not interrupted by a radio cast, nothing interesting would have happened.

Because the verb be is now involved in the antecedent, a morphologically distinct unreal past is also now possible, but now some of the consequents may become grammatically suspect to some speakers:

18. If the day were not interrupted by a radio cast, nothing interesting happened.
19. If the day were not interrupted by a radio cast, nothing interesting would happen.
20. If the day were not interrupted by a radio cast, nothing interesting will have happened.
21. If the day were not interrupted by a radio cast, nothing interesting would have happened.

Many of those would give a native speaker reason to pause and try to figure out exactly what it means. For example, 18 would seem to still mean the same as 14. This ambiguity caused by was vs were disappears using get passives:

22. If the day got interrupted by a radio cast, something interesting happened.
23. If the day got interrupted by a radio cast, something interesting would happen.
24. If the day got interrupted by a radio cast, something interesting will have happened.
25. If the day got interrupted by a radio cast, something interesting would have happened.

or with negation, triggering do support:

26. If the day didn't get interrupted by a radio cast, something interesting happened.
27. If the day didn't get interrupted by a radio cast, something interesting would happen.
28. If the day didn't get interrupted by a radio cast, something interesting will have happened.
29. If the day didn't get interrupted by a radio cast, something interesting would have happened.

So in fact sentence 29 is most like your original, which is my sentence 4:

4. If this day wasn't interrupted by a sudden radio cast, so-and-so would have happened.

What it comes down to in sentence 4, just as sentences 13 and 17 and 25 and 29, it feels much more like an antecedent real past than an unreal one, yet the consequent seems to be completely hypothetical. This isn’t a very common pattern; you probably should not use it lest the reader become confused.

The most common (but by no means exclusive) pattern with a hypothetical consequent is your second version, my sentence 5:

5. If this day hadn't been interrupted by a sudden radio cast, so-and-so would have happened.

And while that version is one that is safe for non-native speakers, native speakers commonly use many other patterns for the antecedent — even with the same consequent.

30. If the radio interrupted, something would have happened.
31. If the radio did interrupt, something would have have happened.
32. If the radio might interrupt, something would have happened.
33. If the radio could interrupt, something would have happened.
34. If the radio could have interrupted, something would have happened.

Some variants are more likely to be heard in casual speech. Other variants like inversion for hypotheticals are more likely seen in literature, especially older or more formal writings. See this ELU question for many more possibilities. Here’s just one that’s particularly interesting as there are no hypotheticals involved whatsoever:

35. If the radio interrupted that day, then something truly incredible will have happened.

Take special note that sentence 35 uses will to indicate a past time, not a future time as it does in so many other cases.

Why does this case of will mean it’s talking about the past not the future? Because it’s also using the perfective aspect, that’s why. Surprise! :) Once it’s perfect, it’s always a completed action. It’s a way of expressing extremely likelihood, something virtually guaranteed to have occurred.

Modal auxiliaries are very complicated things in English, and so are the other auxiliary verbs. Any shortcuts taken in teaching and understanding all this will necessarily always contain simplifications that simply do not apply in all cases actually encountered. In short, they’re convenient fictions at best, early mythologies.

Answer 2

"Wasn't interrupted" is the preterit tense. Its usage here is improper. Since what you're saying is a hypothetical situation that no longer exists as even its condition is in the past (i.e., "would have been"), the pluperfect subjunctive is required. Therefore, the proper way to write that would be:

"If this day hadn't been interrupted by a sudden radio cast, so and so would have happened...."

By the way, while this isn't actually relevant to your question, you should know that in the above sentence "so and so" isn't what native speakers would generally say there. In the vernacular, native speakers say "so and so" to refer to people, and when it's not people that's being referred to, native speakers say "such and such." Since what would've happened is a thing that would've happened, not a person that would've happened, you would say "such and such" instead.