Prepositions are particles that are put in front of clauses, to show their role in the sentence.
Prepositions are normally placed before nouns or pronouns, but they can also be used with infinitive verbs, subclauses, and adverbs of quantity. In some cases a preposition is used before an adverb of location or time. In those cases, the preposition makes the location or time more specific.
The following particles are prepositions: al, anstataŭ, antaŭ, apud, ĉe, ĉirkaŭ, da, de, dum, ekster, el, en, ĝis, inter, je, kontraŭ, krom, kun, laŭ, malgraŭ, per, po, por, post, preter, pri, pro, sen, sub, super, sur, tra and trans:
Independent prepositions
After a preposition there is normally a clause to which the preposition relates. Without a clause following, the preposition would not make sense: sur la tablo, en mia domo, ekster tiu ĉi ĉambro, dum la paŭzo, anstataŭ tio, krom Petro etc.
If words are intended to be left out after a preposition (to be understood through context), the preposition must be used with an E-ending, because the preposition then becomes its own clause, acting as an adverb:
- Li staras apud mi. → Li staras apude. - He is standing beside me. → He is standing alongside.
- Ŝi sidas ekster la domo. → Ŝi sidas ekstere. - She is sitting outside of the house. → She is sitting outside.
- Tio okazis dum la paŭzo. → Tio okazis dume. - That happened during the break. → That happened in the duration.
- Tio okazos post la kongreso. → Tio okazos poste. - That will happen after the congress. → That will happen later.
If the adverb shows a location, it can accept the N-ending to show movement to the location:
- Li sidas ekster la domo. → Li sidas ekstere. → Li iras eksteren. = ...al ekstera loko (al loko ekster la domo). - He is sitting outside the house. → He is sitting outside. → He is going outside. = ...to an outside location (to a place outside of the house).
If in some cases the original clause acts as an adjective, the A-ending is used after the preposition:
- Li loĝas en domo apud mia domo. → Li loĝas en apuda domo. ...en domo apuda. - He lives in a house next to my house. → He lives in an adjacent house. ...in a house next to mine.
But you can also use a location adverb or temporal adverb in those cases: Li loĝas en domo apude. = Li loĝas en domo, kiu troviĝas apude.
For some reason, some prepositions practically never appear with an E-ending or A-ending. For example, we almost never say paroli prie = "talk about that", iri dee = "to go from the designated place", ala veturo = "a drive to the designated place", proa agado = "an action on account of that".