Why accusative in duration before "antaŭ"?

Question

Why does "monatojn" carry the accusative marker "-n" in the following sentence?

Ĉiu diskutota demando estas ja publikigita tri monatojn antaŭ la kongreso.

(Seen in PMEG, which in turn attributes it to "Originala Verkaro, paĝo 460".)

Answer 1

"tri monatoj antaŭ la kongreso" expresses the point in time when the action ("Ĉiu diskutota demando estas ja publikigita") "happens".

According to section "N por tempopunkto" of PMEG, "tri monatoj antaŭ la kongreso" thus acts as a complement and has to either carry the accusative marker "-n" or as a whole has to be prepended by a preposition (a rolvorteton).

• "tri" cannot receive "-n" as it's a number.
• "monatoj" can and does receive the "-n" marker and thus becomes "monatojn".
• "antaŭ la kongreso" is a prepositional phrase within the complement.
  • "antaŭ" itself cannot receive "-n" as it's a preposition.
  • "la kongreso" doesn't receive "-n" because what's modified by "antaŭ" is always in nominative. (As is the case for most prepositions in Esperanto, with place-preposition-used-to-indicate-direction being the prominent and probably only exception.)

Answer 2

There are two time-related constructions. When an action lasts "a long time", you use the prepostion dum (during, for) in Esperanto.

Tiu diskutota demando estas ja disputita dum tri monatoj antaŭ la kongreso.

The question in discussion was argued about for three months before the congress. (The discussion was more or less going on under the whole time-span.)

When something is perceived to happen at "a specific point in time", you use either the accusative or a prepostion (other than dum), usually en (in, at).

Ĉiu diskutota demando estas ja publikigita tri monatojn antaŭ la kongreso.

Every question was indeed published three months before the congress. (The publishing took place at a specific point in time, that was three months before the congress.)

Sometimes you can use a prepostion instead of the accusative

En unu tago… = Unu tagon estis forta pluvo

but the accusative is more common.

Note the use of quotes above for "long time" and "point in time", because there is a lot of overlap.

Mia kapo doloris la tutan tagon.

The day is perceived to be "a specific point in time" and while you can say …dum la tuta tago, the accusative expression is way more common.

The phrase antaŭ la kongreso exists in the sentences only to fix the time-span resp. point in time. If you leave it out, one assumes that now is implied. In the first example this means, that the arguing has been going on for three months before this day (and the verb tense, estas disputita indicates, that the arguing has finished). In the second example, that the questions were published three months ago (and obviously remains published).