If conditions

Third conditional[edit]
"Third conditional" or "conditional III" is a pattern used to refer to hypothetical situations in a past time frame, generally counterfactual (or at least presented as counterfactual). Here the condition clause is in the past perfect, and the consequence is expressed using the conditional perfect.
If you had called me, I would have come.
Would he have succeeded if I had helped him?
It is possible for the usual auxiliary construction to be replaced with were to have + past participle. That used, the above examples can be written as such:
If you were to have called me, I would have come.
Would he have succeeded if I were to have helped him?
The condition clause can undergo inversion, with omission of the conjunction:
Had you called me, I would have come. / Were you to have called me, I would have come.
Would he have succeeded had I helped him? / Would he have succeeded were I to have helped him?
Another possible pattern (similar to that mentioned under the second conditional) is if it hadn't been for... (inverted form: had it not been for ...), which means something like "in the absence of ...", with past reference. For clauses with if only, see Uses of English verb forms § Expressions of wish.
For the possible use of would in the condition clause, see § Use of will and would in condition clauses. Occasionally, with a first person subject, would is replaced with should. In the main clause, the auxiliary would can be replaced by could or might, as described for the second conditional.
If only one of the two clauses has past reference, a mixed conditional pattern (see below) is used.