The past unreal conditional's structure has two clauses. There is an adverb clause normally starting with If. There is also an independent clause.
Like all conditionals, the adverb (IF) clause has the condition, and the Independent clause contains the result.
In the past unreal conditional, The adverb clause is in the past perfect tense, and the independent clause is in the present perfect tense including a modal, typically would, or could.
If I had given him his medicine, he would have lived.
He would have lived if I had given him his medicine.
If I had ruled Spain, I wouldn't have wasted my time on conquering America.
I wouldn't have wasted my time conquering America if I had ruled Spain.
If I had been born in another country, would you still have fallen in love with me?
Notice in the above examples the use of the past perfect tense in the dependent (adverb) clauses, and the use of the present perfect with modal (in this case would) in the result clauses.
The clauses have been color coded. The independent clauses are in a different color while the adverb clauses are still in black.
Present real Conditional (0)
Future real conditional (1)
Present/Future UnReal Conditional (2)
Past unreal conditional (3)
Real means that if the condition is met, the result happens or will happen.
Unreal means that the condition will not be met, did not happen, or that it is very unlikely to happen.
When to use each kind of conditional
For generalities, you should use a present real conditional.
For plans that have requirements or possible setbacks, use a future real conditional.
For wishes, dreams, and speculation that is doubtful use a present/future unreal conditional.
For regrets, things you'd like to have done differently, and any past events you want to change (but you can't since you're still working on that time machine!) use a past unreal conditional.
Where is past real?
Well there is no past real tense because no matter how much Doctor Who we watch... The TARDIS is not going to materialize on your street corner. We can't go back and change the past. If we could, we would, but we can't so we won't. :-)Punctuation
The punctuation of conditionals really isn't complicated.
First like any sentence, you'll need a period(.), exclaimation point (!), or question mark( ?) at the end.
The special punctuation is true of any sentence with an adverb clause. If the dependent adverb clause is before the independent clause, you need to put a comma after the adverb clause. If the independent clause is before the adverb clause, then there is no comma.
Dependent, Independent.
or
Independent Dependent.
