If + subject + had + past participle +
other words, subject + would have ('ve) +
past participle + other words.
OR
Subject + would have ('ve) + past
participle + other words if + subject +
had + past participle + other words.
(This form is used for BE and other verbs.)
Examples:
If he had been here yesterday, he would've
helped you. / He would've helped you if he
had been here yesterday.
(He wasn't here yesterday, so he couldn't
help you.)
If I had had enough money, I would've
traveled around the world. / I would've
traveled around the world if I had had
enough money.
(I didn't have enough money, so I couldn't
travel around the world.)
If cars had cost less, I would've bought
a new one. / I would've bought a new car
if they had cost less.
(New cars cost too much for me, so
I couldn't buy one.)