Pro marks a cause, reason, or motive: the situation named after pro helps explain why something happens. In La matĉo estis nuligita pro la pluvo, the rain exists first and causes the cancellation. This backward-looking logic distinguishes pro from por, which normally points forward to a goal, intended use, or beneficiary.
Cause: what produced the result?
Use pro for events, conditions, and circumstances that cause another state or event.
La trajno malfruis pro teknika problemo, sed ni tamen alvenis antaŭ tagmezo.
The train was late because of a technical problem, but we still arrived before noon.
Pro la densa nebulo la flughaveno nuligis plurajn flugojn.
Because of the dense fog, the airport canceled several flights.
Kial la strato estas fermita? — Pro riparo de akvotubo.
Why is the street closed? — Because of a water-pipe repair.
The complement is unmarked: pro la problemo, pro la nebulo, pro riparo. Pro itself identifies the causal role, so accusative -n is neither needed nor permitted on an ordinary complement.
The cause may be physical, social, emotional, or abstract.
Ŝi tremis pro malvarmo kaj tuj surmetis pli dikan jakon.
She was shivering from the cold and immediately put on a thicker jacket.
La kandidato estis kritikita pro manko de konkreta plano.
The candidate was criticized for lacking a concrete plan.
English uses “because of,” “from,” “for,” and “due to” across these contexts. Esperanto pro makes their shared causal structure explicit.
Motive: the reason for a deliberate action
A motive is a cause inside an agent’s decision. Pro can therefore explain why someone acts.
Mi demandis nur pro scivolemo; vi ne devas respondi.
I asked only out of curiosity; you do not have to answer.
Li ne protestis pro timo perdi sian laboron.
He did not protest for fear of losing his job.
Ili volontulis pro sincera deziro helpi la najbarojn.
They volunteered because of a sincere desire to help the neighbors.
With inner states, el can offer a different viewpoint. El scivolemo presents curiosity as the inner source from which the act arises; pro scivolemo presents it neutrally as the motive or reason. Both are established, and context decides which image is more useful.
De also occurs with some physical or emotional causes, such as paliĝi de timo. This is accepted variation, especially in fixed collocations. Pro remains the clearest general marker when an explicit cause–result relation matters.
Pro versus por: reason versus purpose
This is the central decision for English speakers because English “for” can express both.
Mi restis hejme pro la pluvo, sed mi uzis la tempon por fini la raporton.
I stayed home because of the rain, but I used the time to finish the report.
The rain caused the decision, so it takes pro. Finishing the report was the intended use of the time, so it takes por.
| Question | Relation | Preposition |
|---|---|---|
| Why did it happen? | existing cause or motive | pro |
| What is it meant to achieve? | purpose or goal | por |
| Who is it intended for? | beneficiary or recipient | por |
Ni ŝparis monon por la vojaĝo, sed ni prokrastis la vojaĝon pro malsano.
We saved money for the trip, but we postponed the trip because of illness.
La kuracisto preskribis medikamenton por mildigi la doloron, sed mi ĉesis ĝin preni pro kromefikoj.
The doctor prescribed medicine to relieve the pain, but I stopped taking it because of side effects.
In medikamento por mildigi la doloron, relief is the intended result. If one says ĝemi pro la doloro, the pain is the cause of the groaning. See the full por or pro decision guide.
Where motive and goal overlap
Someone can act because they desire a future result. Foundational Esperanto therefore uses pro in some sentences that could also take por, especially when the goal is conceptualized as the motivating cause: batali pro libereco “fight for freedom.”
Multaj homoj manifestaciis pro pli sekuraj laborkondiĉoj.
Many people demonstrated for safer working conditions.
Here safer conditions are both the desired goal and the motive that brings people into the street. Por pli sekuraj laborkondiĉoj is also possible and more directly presents the goal. In contemporary neutral usage, por is generally the clearer first choice for a pure purpose; pro adds a reason-or-cause viewpoint.
This is accepted semantic overlap, not a license to interchange the words everywhere.
Thanks, blame, praise, and reaction
The thing thanked, blamed, praised, or punished for is naturally the reason for the reaction.
Dankon pro via rapida respondo; ĝi multe helpis nin.
Thank you for your quick reply; it helped us a lot.
La trejnisto laŭdis la teamon pro ĝia pacienco.
The coach praised the team for its patience.
La firmao pardonpetis pro la erara fakturo.
The company apologized for the incorrect invoice.
Por is also widespread in thanks, especially dankon por .... Pro transparently marks the reason for gratitude and is an excellent neutral choice. Do not treat every English “for” alike: the frame depends on whether the following phrase is a reason, purpose, or beneficiary.
Pro tio, ke ... and ĉar
Before a finite ke clause, neutral Esperanto normally inserts tio.
La lernejo fermis la korton pro tio, ke la planko estis glacia.
The school closed the courtyard because the ground was icy.
The compact conjunction ĉar often says the same thing more lightly:
La lernejo fermis la korton, ĉar la planko estis glacia.
The school closed the courtyard because the ground was icy.
Pro tio, ke foregrounds the circumstance as the cause; ĉar simply introduces a causal explanation. Bare pro ke is not the standard construction. Cause clauses covers the full choice among ĉar, pro tio, ke, and related connectors.
Pro kio? asks “because of what?” and expects a cause phrase. Kial? is the more general “why?”
Pro kio vi ŝanĝis la daton? — Pro la malhavebleco de la salono.
Because of what did you change the date? — Because the hall was unavailable.
Price and exchange: an accepted traditional use
Pro is attested in payment, purchase, and sale expressions, where the payment motivates the transfer.
La kolektanto aĉetis la malnovan afiŝon pro kvindek eŭroj.
The collector bought the old poster for fifty euros.
This is grammatical and part of established usage. Modern neutral Esperanto, however, normally prefers por for a price—aĉetis ĝin por kvindek eŭroj—and kontraŭ when the exchange of two things is central.
Mi interŝanĝis mian malnovan biciklon kontraŭ uzita fotilo.
I exchanged my old bicycle for a used camera.
The distinction is pedagogical, not a ban: price pro is accepted but less usual; price por is the contemporary default; kontraŭ presents reciprocal exchange.
Word formation and historical limits
Unlike pri, pro rarely appears as the standalone derivatives proa or proe; neutral Esperanto uses pro tio, kaŭza, or a fuller phrase. Some older compounds with pro- express acting on someone’s behalf, but they are not a productive model learners should freely imitate.
Historical texts also contain pro meaning “instead of,” probably under Latin influence. That use is not recommended today: use anstataŭ. Keeping this separate from modern cause and motive prevents an attested old usage from being mistaken for a current option.
Norm and register
Causal and motivational pro is foundational and neutral. Goal-like motive uses are established, though por is clearer for pure purpose. Price pro is accepted but less common than por in present-day neutral usage. Pro = anstataŭ is historical and should not be imitated.
Common Mistakes
Using por for an existing cause
❌ La pikniko estis nuligita por la pluvo.
Incorrect — the rain caused the cancellation; it was not its purpose.
✅ La pikniko estis nuligita pro la pluvo.
The picnic was canceled because of the rain.
Using pro for a pure purpose
❌ Mi iris al la vendejo pro aĉeti panon.
Incorrect — buying bread is the intended purpose, and pro does not introduce this infinitive.
✅ Mi iris al la vendejo por aĉeti panon.
I went to the shop to buy bread.
Adding -n after pro
❌ La flugo malfruis pro la fortan venton.
Incorrect — pro already marks the causal role.
✅ La flugo malfruis pro la forta vento.
The flight was delayed because of the strong wind.
Putting ke directly after pro
❌ Ŝi ĝojis pro ke ĉiuj alvenis sekure.
Nonstandard — use pro tio, ke or ĉar before a finite clause.
✅ Ŝi ĝojis pro tio, ke ĉiuj alvenis sekure.
She was glad that everyone arrived safely.
Extending the historical “instead of” meaning
❌ Mi laboros pro vi dum vi ferios.
Wrong for ‘instead of you’; this normally means ‘because of you.’
✅ Mi laboros anstataŭ vi dum vi ferios.
I will work in your place while you are on vacation.
Key Takeaways
Use pro for the cause or motive that explains a result, with an unmarked complement. Use por for a goal, intended use, or beneficiary. Pro tio, ke introduces a full causal proposition, while ĉar is the lighter conjunction. Traditional price pro remains grammatical, but por is the modern default and kontraŭ emphasizes exchange.
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Start learning Esperanto →Related Topics
- PorB2 — Use por for an intended beneficiary, purpose, use, result, exchange, or the goal toward which an action is directed.
- ElA2 — Use el for movement from an interior, origin, material, components, and selection from a defined group.
- DeA2 — Use de for movement or development away from a source and for relationships such as possession, authorship, composition, time, and passive agency.
- JeB1 — Use je for conventional clock-time, measure, body-part, and abstract relations when no more specific preposition expresses the intended role.
- Por or Pro?B1 — Choose por for intended goals, beneficiaries, and exchange, and pro for causes, motives, and reasons already producing an effect.
- Cause ClausesA2 — Explain reasons and motives with finite ĉar clauses while distinguishing them from pro phrases, tial, and coordinating links.