For example:

Dankon pro helpi min

I know that it is grammatically incorrect to say “Dankon pro vi helpis min”, because a complete fraze cannot follow a preposition. You would need to say “Dankon pro tio, ke vi helpis min”.

However, this is very long winded and tedious, so I would like to just say “Dankon pro helpi min.” And I am pretty sure that this is correct, because all prepositions can be followed by an infinitive verb, right? Ex. “Interesi pri lerni esperanton”.

My only problem is that I have almost never seen this before! I usually see “Dankon por helpi” instead. However, this doesn’t make sense to me because “por” means “in order to, so that” and “pro” means “because of”.

Is there some weird rule where pro can’t be followed by an infinitive verb? Is this a stylistic preference? If so, what is favorable about por in this context? Am I wrong about the meaning of pro and por? If so, what is the difference between them?

Dankegon pro klarigi!

  • Thanks because of (for) explaining = Dankon pro la klarigado.
    – Joop Eggen
    Dec 17, 2021 at 11:29

3 Answers 3


And I am pretty sure that this is correct, because all prepositions can be followed by an infinitive verb, right? Ex. “Interesi pri lerni esperanton”.

I think this is debatable. PMEG has a long article about it. The gist is that although it is logical and arguably grammatically correct to use an infinitive with any preposition, in practice there is a sort of taboo about doing it apart from with the four prepositions por, anstataŭ, krom and sen because it can be misunderstood. So that is likely why you don’t see it very often. It is effectively considered bad style. Instead, people generally prefer to make the action into a noun. So, as suggested by Eduardo, a more natural way of expressing your sentence could be:

Dankon pro via helpo.

Please see also this question which has some more suggestions for alternatives to using an infinitive.


Following any preposition with an infinitive is generally discouraged. Zamenhof asserted several times that one should follow a preposition with a noun form instead of an infinitive:

[…] la esprimojn “li faris ĉion sen ridi” aŭ “li restis du tagojn sen manĝi” mi ne konsilus al vi uzi. […] Sed anstataŭ “sen ridi” aŭ “sen manĝi” ni povas ja tre bone diri “sen rido”, “sen manĝo” aŭ “neniom ridante”, “nenion manĝante”.

Ĉiu prepozicio, laŭ sia logika esenco, povas esti uzata nur antaŭ substantivo. Sekve se antaŭ vorto, kiu havas verban sencon, ni deziras uzi prepozicion, ni devas doni al tiu verbo senca vorto la formon de substantivo; ekzemple: anstataŭ “kun saluti”, “sen respondi” ni devas diri “kun saluto”, “sen respondo”.

However, Zamenhof also suggested that a verb can follow a preposition only when "necessary"…

Prepozicion antaŭ verbo mi konsilus uzi nur en okazo de neceseco, se alie ni ne povas bone esprimi nian penson.

… and left room for this usage to be judged by the Akademio (then-"Lingva Komitato"):

Se vi trovas, ke estus necese permesi la uzadon de ĉiu prepozicio kun infinitivo, […] vi povas peni akiri por tio la oficialan pervoĉdonan decidon de la Lingva Komitato.

Zamenhof justified the use of infinitives after specific prepositions (por, anstataŭ) by arguing that

  1. an infinitive, after these words, conveys a substantially different meaning from the noun form;
  2. these words, before an infinitive, are less like prepositions and more like conjunctions.

[L]a vortoj “por” kaj “anstataŭ”, uzataj antaŭ infinitivo, havas la sencon ne de pura prepozicio, sed preskaŭ de konjunkcio, kaj en tiuj okazoj la uzado de substantivo apud ili estas ne ebla; ekzemple, en la frazo “anstataŭ stari li sidas” ni ne povas anstataŭigi la formon “stari” per “staro”, dum ĉe ĉiu alia prepozicio pura ni ĉiam povas uzi la verbosencan vorton en formo de substantivo (ekzemple, “sen ia diro” anstataŭ “sen ion diri”).

Nowadays, krom and perhaps sen are also considered valid before an infinitive; PIV describes both as "(uzebla ankaŭ kun inf[initivo])" [krom, sen], and PMEG lists them together with por and anstataŭ in this regard.

Furthermore, PMEG notes that infinitives are more and more often seen after pri, pro, dum, post, and so on. Theoretically any preposition can be followed by an infinitive, and Esperantists' aversion to this usage is "essentially arbitrary".

In conclusion: It is not customary to follow pro with an infintive verb, however it has never been explicitly disallowed. There are, however, a great number of ways to write a phrase instead of with a preposition + infinitive.

  • I agree. You can think that participles are basically adjectives (which you can turn to adverbs if needed). It is natural to associate time with these, thus we have ridanta, ridinta, ridonta etc. Infinitives behave more like nouns, so the idea of time does not sit, rather different prepositions do. But then why not use nouns in the first place? So instead of sen ridi say sen rido. Perhaps this was behind Zamenhof's reasoning. Dec 22, 2021 at 13:00

dankon pro via helpo, danko pro la klarigo estus naturaj, simplaj manieroj tion diri.

pro estas prepozicio kaj post ĝi vi uzas substantivon, -o vorton. Ne, vi ne povas uzi rekte infinitivon. Vi tamen povas enkonduki frazon per pro tio ke ..., ekzemple:

Mi dankas (vin) pro tio, ke vi klarigis tion al mi.

Dankon pro tio, ke vi helpis min.
  • Tute prava. Estas nur raraj esceptoj (por) en Esperanto.
    – Joop Eggen
    Dec 17, 2021 at 11:28

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