The first special model begins with but for:
But for the rain, we should go to the country.
Если бы не дождь, мы поехали бы загород.But for my illness, I should have graduated last year.
Если бы не моя болезнь, я бы закончил институт в прошлом году.The second special model begins with if it were not for:
If it were not for him, they would fly to Prague for their holiday.
Если бы не он, они бы полетели в Прагу в отпуск.If it had not been for my work, I would have gone to the theater with you.
Если бы не моя работа, я бы сходил с тобой в театр.