English · B2 · grammar · 5 minutes
Third conditional
Imagine a different past and its unreal past consequence.
Understand the choice
Both clauses refer to a past that cannot now change. The construction supports reflection, criticism, regret, and analysis of causes without asserting the imagined history.
Core rule: Third conditional uses if + had + participle and would/could/might have + participle.
Notice it in context
If we had left earlier, we would have caught the train.
Si hubiéramos salido antes, habríamos alcanzado el tren.
Had left places the unreal condition before the missed result; would have caught gives its imagined consequence.
She might have accepted if they had offered remote work.
A remote-work offer could possibly have changed her past refusal.
Might have weakens certainty; had offered states unreal condition.
If I had known about the closure, I could have taken another route.
Knowledge of the closure would have enabled a different route.
Could have expresses unreal past ability.
What to remember
- Both perfect forms need participles, not simple past forms.
- The if-clause may follow the result without a comma in ordinary punctuation.
Common trap: Do not put would have in the standard if-clause.