Type III Conditionals
Form
IF + ACTION , CONSEQUENCE
IF + PAST PERFECT , WOULD + HAVE + PARTICIPLE
Type III (Third) Conditionals are often described as being constructed of Past Perfect, Would + Present Perfect or sometimes even a Conditional Perfect. No such tenses exist. Remember, Would is a Modal verb and is always followed by an infinitive. In this structure therefore, HAVE does not change for the third person as it is to be used as an infinitive.
Function
Type III (Third) Conditionals are often called UNREAL CONDITIONALS. It is impossible to have a conditional action or consequence in the past, as the past is complete, therefore third conditionals are the complete oppositie of reality.
Impossible or unreal consequences of an alternative past:
If I had been born in America, I would have been American.
I would have been American IF I had been born in America.
We often use third conditionals to talk about regret:
If I hadn't been driving so fast, I wouldn't have hit that tree.
You wouldn't have been so tired if you had gone to bed early.
If I had seen the beggar, I would have given him some money
Related topics
Past Perfect form & function
Would + Infinitive
Type 0 Conditionals
Type I Conditionals
Type II Conditionals
Mixed Conditionals