When should use the -n ending?

Explanation

In Esperanto, the ending -n indicates the accusative form. This ending can appear on nouns, adjectives, personal pronouns, correlative words (which end in -u, -o, -a, and -e), and adverbs with the ending -e, which indicate a location. The accusative must be used in the following situations:

1. to show the direct object of a verb. In Esperanto that allows the word order of a sentence to be changed without changing the meaning.
Ŝi vidas lin. - She sees him.
Ŝin vidas li. - He sees her.
Li vidas ŝin. - He sees her.
Lin vidas ŝi. - She sees him.

2. instead of prepositions to show time, measurement etc.
Mi dormis dum unu horo. - Mi dormis unu horon. (I slept for one hour.)
En lundo mi vizitos vin. - Lundon mi vizitos vin. (I'll visit you on Monday.)
En la 22-a de junio mi venos. - La 22-an de junio mi venos. (I'll come on June 22nd.)
Mi estas je 20-metra distanco de vi. - Mi estas 20 metrojn for de vi. (I'm 20 metres away from you.)
Li estas je du metroj alta. - Li estas du metrojn alta. (He's two metres tall.)

3. to show direction or destination of movement.
Mi kuras en la arbaro. - I run in the forest.
Mi kuras en la arbaron. - I run into the forest.
Mia amiko iras trans la strato. - My friend goes on the other side of the street.
Mia amiko iras trans la straton. - My friend goes across the street.
Li saltas sur la tablo. - He jumps on the table.
Li saltas sur la tablon. - He jumps onto the table.

Also after adverbs that indicate location.
Mi estas hejme. - I'm home.
Mi iras hejmen. - I go home.
Vi estas tie. - You're there.
Vi kuras tien. - You are running over there. (to that place)

Accusative after a preposition

There are prepositions that have two meanings; with a nominative they indicate the place where something is found, with an accusative they show the destination something is moving to. These prepositions are: sur, sub, en, apud, antaŭ, malantaŭ, post, inter, trans, ekster, super, ĉirkaŭ, kontraŭ.
sur la tablo - on the table
sur la tablon - onto the table
sub la domo - under the house
sub la domon - (to) under the house

But there are prepositions after which an accusative is never used: al, ĝis, de, el ,da, pri, pro, por, per, kun, sen, je, dum, laŭ, malgraŭ, and preferably not with: tra, preter. After these prepositions, generally only the basic form without -n is used.
pri la knabo - about the boy
al la urbo - to the city
kun mia amiko - with my friend

Be careful!

If a noun has the -n ending, then all adjectives, possessive pronouns and correlative words that relate directly to the noun must also have the same ending. The -n ending is also written after the plural ending -j:
Mi aĉetis tiun grandan domon. - I bought that big house.
Mi aĉetis tiujn tri grandajn domojn. - I bought those three big houses.
Mi iras en mian belan domon. - I go into my beautiful house.
Mi promenis tre longan tempon. - I walked for a very long time.
Mi promenis kelkajn tagojn. - I walked for a few days.
Iun belan tagon mi revenos. - I'll come back one fine day.

Be careful about using the accusative, since the addition of the -n ending can completely change the meaning of the sentence. Analyze the following sentences:
Mi ŝatas manĝi tion pli ol vi. - I like to eat that more than you do.
Mi ŝatas manĝi tion pli ol vin. - I like to eat that more than I like eating you.
Mi amas ŝin same forte kiel vi. - I love her as strongly as you do.
Mi amas ŝin same forte kiel vin. - I love her as strongly as I love you.
Vi farbas la domon ruĝan. - You're painting the red house.
Vi farbas la domon ruĝa. - You're painting the house red.

Exercises

Level 1 Level 2