a. The driver of the car would have crashed, had he not been concentrating.

or The driver of the car would have crashed, if he had not been concentrating.

b. The driver of the car would have crashed, if he weren't concentrating.

or The driver of the car would have crashed, were he not concentrating.

c. The driver of the car would have crashed, if he wasn't concentrating.

Please explain the differences between a & b & c, if you see any?

Ta,

Eng
There's no difference in meaning between a & b. Note, however, that b is acceptable only in an informal style (where the simple past were is sometimes used instead of the past perfect had been)

c is incorrect. The "would have crashed" part in the main clause requires that the condition is counterfactual. Therefore the verb in the if-clause must be either had been or were. The use of wasn't suggests that the condition isn't counterfactual (at least we cannot verify that at this point).

Consider this example

The driver crashed the car if he wasn't concentrating.

(we can't verify whether the driver was concentrating or not so the condition isn't counterfactual. The sentence simply says that the driver crashed the car when he wasn't concentrating and vice versa)
IvanhrThere's no difference in meaning between a & b. Note, however, that b is acceptable only in an informal style (where the simple past were is sometimes used instead of the past perfect had been) c is incorrect.)
Can't we say there is a difference between a & b, this difference being that b suggests the concentrating is still happening?

And with your sentence, I believe it suggests not that he definitely crashed the car but that if he wasn't concentrating, which suspect is so, then the result is definitely that he crashed. Do you not agree with this?
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English 1b3Can't we say there is a difference between a & b, this difference being that b suggests the concentrating is still happening?
No. If that were the case, the sentence would read

The driver would crash if he weren't concentrating.

English 1b3And with your sentence, I believe it suggests not that he definitely crashed the car but that if he wasn't concentrating, which suspect is so, then the result is definitely that he crashed. Do you not agree with this?
Basically, that's what I said (but admittedly I didn't use the word definitely)