The “essence” of -as, -is, -os, -us alone

Question

This is a very primitive question but I don't know where else to look for an answer. I tried ESPDIC and Tekstaro with some queries but without success. I wonder if Esperanto has some neutral verb or some accepted pattern of speech to be used in a situation like

They say that he {studies|studied|will study|would study} Esperanto but I don't know if he {does|did|will|would}.

The closest I came up with myself (apart from the obvious ...ĉu tio veras) is

Oni diras, ke li studas/-is/-os/-us Esperanton, sed mi ne scias, ĉu li faras/-is/-os/-us tion.

This pattern has limited usability, though, as one can't use this expression to make standalone statements like “Yes, I did.” or “Would you?” or “If you will then I will”. I thought, given that one can take the infixes -ej-, -eg-, -il- etc. for roots of their own, maybe there's a way of using the suffixes -as, -is, -os, -us without any specific verb root, too (somehow), or using some stub root that does not really bring in any additional meaning.

Of course it's perfectly OK if there's no such thing, but maybe I'm just missing something very obvious?

Answer 1

The stub root is just far-.

Your translations, ...ĉu tio veras. ...ĉu li far*s tion. are correct. You could also say mi ne scias ĉu vere. I would avoid ending the sentence with ĉu. as it would probably be interpreted as a tag question.

• Jes ja. Yes I did [or similar statement]. [lit., Yes indeed.]
• Ĉu vi farus tion? Ĉu vi agus tiel? Would you do that [in that situation]?
• Ĉu vi faru tion? Would you do that? [request]
• Se vi faros, mi faros. If you will then I will.
• Mi luas aŭton. Ĉu vi? I'm hiring a car. And you?
• Li instruis min. Ĉu vin? He taught me. Did he teach you?

It is uncommon for as, is, os to be used as free-standing words, and that usage has a very slangy or very rhetorical sound. Some poets (e.g. Grabowski) used them as short forms for estas, estis, estos.

• Mi estis, -as, kaj -os Parizano. I was, am and will be a Parisian.