"I would not X if I didn't Y" vs "I would not X if had not Yed"

Question

What are any differences between these two conditionals in their grammaticality, meaning, connotation, and formality?

1. I would not be writing to you so soon to ask about my interview result if I did not receive a call for employment from another company to whom I have applied.

2. I would not be writing to you so soon to ask about my interview result if I had not received a call for employment from another company to whom I have applied.

   Are those both grammatically permitted? Are they 100% interchangeable? When should you use one and when the other? How does changing the expected sequence of tenses affect the grammar or meaning or usage? Which sounds more natural, if either?

Answer 1

When we use simple past tense after the "if" in a conditional sentence, we are talking about something hypothetical happening now or in the future, which has a future result. (2nd conditional)

• If I won the lottery I would buy a big house
• If I didn't have to work so much, I would play more sport.

But in this case, the call was received in the past, and so the hypothetical situation cannot happen now or in the future.

When we want to hypothesise about something that happened in the past, then we have to use past perfect.

The most commonly taught form is the 3rd conditional, where the consequence is also in the past:

• If I hadn't received a call from another company, I would not have written to you so soon.

In this case, however, it's a mixed third/second conditional, where the consequence is happening now:

• If I hadn't received a call from another company, I would not be writing to you so soon.

Answer 2

Both of these sentences are examples of conditionals, and these is a nice post about the different types of conditionals. The reason "if I didn't receive" doesn't work here is that you actually received the call, and the form of the conditional you need for an "alternative past" (where you didn't receive the call) is the one which utilizes the past perfect tense.

Consider these examples with a past simple conditional:

My friend is pretty depressed. I would feel the same way if I got rejected from every college I applied to. Thankfully, that's not the case.

If I didn't already know you, I would think you're a total jerk after what you said at dinner. But, after 10 years of living together, I realize you were just having a bad night.

I would go to the beach all the time if I lived a little closer. Unfortunately, it's a 3-hour drive one way.

All of them refer to an alternative present rather than an alternative past.