VERBS (continued), -us.
Sometimes we want to express a "supposition", to say that something
"would" take place, supposing that something else, which is not likely
to occur, were to do so, or that something "would have" taken place if
something else which did not occur had done so. In this case the verb
must end with "-us", as, If I were well (which I am not) I should be
happy (which also I am not), "Se mi estus sana, mi estus felicxa". If
he knew (supposition) that I am here (a fact) he would immediately come
to me (supposition), "Se li scius, ke mi estas tie cxi, li tuj venus
al mi". Compare the two following sentences:-- (i.). "Kvankam vi estas
ricxa, mi dubas, cxu vi estas felicxa", Though you are (in fact) rich, I
doubt whether you are (in fact) happy, (ii.). "Kvankam vi estus ricxa,
mi dubas, cxu, vi estus felicxa", Though (supposing that) you were rich,
I doubt whether you would be happy.