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
If he paid
I would stay.
Si me lo trajera
If he brought
it to me,
I would be happy.
no tendríamos hambre.
we wouldn't be hungry.
nos compraríamos la casa.