-us: would, on both halves of an unreal if

-us says what would happen; -u says what somebody wants to happen. Neither ending changes for person or tense, and both go on the verb root like any other ending.

-us goes on both halves

English marks an unreal sentence twice, with two different tools: a past tense in the if half and would in the other. Esperanto uses one ending, twice:

• Se mi havus tempon, mi helpus vin. - If I had time, I would help you.
• Se mi estus reĝo, mi donus al vi ĉion. - If I were king, I would give you everything.

Do not copy the English past into the if half. Se mi havis tempon is a real past: whenever I had time, back then.

• Se mi havis tempon, mi legis. - If (whenever) I had time, I read.

kvazaŭ: as if

Kvazaŭ introduces something imagined, so it normally takes -us as well:

• Li parolas, kvazaŭ li scius ĉion. - He talks as if he knew everything.
• Ŝi rigardis min, kvazaŭ ŝi ne konus min. - She looked at me as if she did not know me.

Open conditions keep their tense

-us is for a condition that is contrary to fact or unlikely. One that may well come true takes the ordinary tense, in both halves:

The first row is the one to notice. English says if you come, present, about the future; Esperanto says venos, because the coming is in the future. The third row is a plain general truth, so it takes the present.

-us has no tense

There is no past conditional ending. The same sentence covers now and then:

• Se mi scius, mi dirus al vi. - If I knew, I would tell you. / If I had known, I would have told you.

Context settles it, or an adverb such as tiam (then):

• Se mi tiam scius, mi dirus al vi. - If I had known then, I would have told you.

When the past must be explicit, estus plus an -inta participle does it: mi estus dirinta al vi, I would have told you. It is correct and heavy; compound tenses has the full set.