If the
probability that the condition materialises is smaller
the Irrealis is to be used. In English you have in the
first part sentence - the if-sentence - the simple past,
in the second part of the sentence the conditional present.
If he had(= simple past) money
I would be (= conditional present)
happy (he thinks).
In Spanish you have the subjuntivo
imperfecto in the first sentence (the si-sentence)
and the condicional
in the second part of the sentence.
Si me pagara
(pagase) más,
me quedaría.
If he paid
me more,
I would stay.
Si me lo trajera
(trajese),
estaría feliz.
If he brought
it to me,
I would be happy.
Si comiéramos
(comiésemos),
no tendríamos hambre.
If we
ate something,
we wouldn't be hungry.
Si fuéramos
(fuésemos) ricos,
nos compraríamos la casa.
