The grammatical ending N is called an accusative ending or simply an accusative. It can be added as an ending to words of various types:

• nouns: domo → domon, hundo → hundon, virino → virinon, seĝoj → seĝojn, ekskursoj → ekskursojn
• adjectives: ruĝa → ruĝan, granda → grandan, virina → virinan, verdaj → verdajn, knabaj → knabajn
• personal pronouns: mi → min, ĝi → ĝin, ili → ilin, oni → onin, si → sin
• tablewords (correlatives) ending in U, O, and A: kiu → kiun, iu → iun, ĉiuj → ĉiujn, kio → kion, ĉio → ĉion, ia → ian, nenia → nenian, tiaj → tiajn
• location adverbs and location correlatives in E:hejme → hejmen, tie → tien, ie → ien

The N-ending is always placed after a J-ending, where one is present: domojn, hundojn, virinojn, ruĝajn, grandajn, virinajn, kiujn, kiajn.

If a noun has the N-ending, then all adjectives and table words in U and A forms, which are epithets to that noun (that is, which describe the noun) should also have the N-ending.

Objective predicatives, however, should not have the N-ending: Mi refarbis la flavajn seĝojn blankaj.

The N-ending can show:

• object
• measurement
• point in time
• direction
• other meanings

Object

An object is the thing that is directly influenced by an action. The direct object is shown using the accusative N-ending. That enables use of various word orders.

Each of the following sentences has basically the same meaning: kato mordas hundon; kato hundon mordas; mordas kato hundon; mordas hundon kato; hundon kato mordas; hundon mordas kato (in each case the cat is the one who is biting while the dog is suffering the bite. On account of the N-ending each one of the equivalent variants is clearly understood. The word order only depends on style and taste.

Mi amas vin; mi vin amas; vin mi amas; vin amas mi; amas mi vin; amas vin mi. All six variants basically have the same meaning: The action amas originates with "mi", and the love goes to "vi".

A sentence with an object can be transformed into a passive sentence. Then the object becomes a subject.

Esti (to be) and similar verbs are not actions directed towards something. The part of the sentence which relates to esti is not an object but a predicative, which never has an N-ending: Tio estas tri seĝoj. Mi estas kuracisto. Ŝi fariĝis doktoro. Mia patro nomiĝas Karlo.

The subject of a verb can be placed after the predicate. This word order is used very frequently with some verbs. The N-ending shouldn't be used with these subjects:

Measure

Adjects and supplements of measure often have an N-ending.

Measurement of time

An N-ending on an expression involving time can show measurement of length of time, duration, or frequency. These expressions answer the questions: kiel longe? (how long?), (dum) kiom da tempo? (for how long?), kiel ofte? (how often?), and so forth.

An N-clause measuring time is usually an adject of a verb:

An N-clause measuring time can also be a supplement to an adjective or an adverb:

A time-indicating phrase with N can also be combined with a temporal post or a temporal antaŭ to show the time: Du tagojn post tio ŝi forveturis Norvegujon. Pasis du tagoj post "tio".

Various measures

Other measures work the same way as measures of time. It could be a measurement of spatial length, height, width, distance, depth, weight, cost, etc. They answer the questions how much?, how many?, how far?, how long?, how high?, how deep?, how heavy?, etc.:

Measure without a role marker

A measurement can also appear in a sentence function that does not have a role marker: Dek jaroj estas tre longa tempo. (Ten years are a very long time.) Dek jaroj is the subject here. Pasis du tagoj. (Two days went by) Du tagoj acts as a subject.

Point in time

A clause with an N-ending can be a circumstantial complement (adjekto) that shows a point in time. This N-adject answers the questions: when?, on what date?, on what day?, in what year?, which time?, and so forth. One may say, that this sort of N-ending substitutes for a preposition of time, usually en (in):

With days of the week, the accusative noun indicates a specific, known day: dimanĉon = "on a certain known Sunday", even if la isn't used. The adverbial form of the weekday normally shows that we are talking about those type of days: dimanĉe "on Sundays, on every Sunday": Mi alvenos en Lyon lundon la 30-an de Aŭgusto.

In expressing time of day the word je, should be used, especially if the word horo (hour) estas is left out, to avoid confusing the hour with the date:

Point in time without a grammatical marker

A point in time can also appear in a sentence function without a role marker: Hodiaŭ estas sabato, kaj morgaŭ estos dimanĉo. Sabato and dimanĉo are the grammatical subject of the sentence.

Direction

N-adjects and N-supplements can show direction. In those cases, they answer the questions to which place?, in which direction?, and so forth.

N-ending used alone

The directional N-ending without a preposition is used only to express going inside of something. We do not say iri muron, iri kuraciston, but rather iri al muro, al kuracisto. In effect, a directional N by itself is in most cases used only with place names (mainly names of cities).

N with en, sur and sub

A directional N-ending is most commonly used with en (in), sur (over), and sub (under), the three most important prepositions of location. When en, sur, and sub show simple position, they are used without the N-ending. But when showing that something is moving to that place, the phrase must be completed with a role marker that shows direction. In theory, prepositions like al (to) (al en, al sur, al sub) may be used, but in practice, the N-ending is always used instead:

With locational prepositions other than en (in), sur (on), and sub (under), the directional N-ending isn't normally used; instead, the context shows the movement in a direction. But the directional N can be with other prepositions of location, if it helps make the meaning clear:

In some cases, the directional N-ending is not normally used, because the destination of the phrase is understood only through context, but not stated. This expression would have an N-ending, if it were included in the sentence:

However, it would not be wrong to say sub la kverkon (under the oak) and antaŭ min (in front of me, before me), because these expressions can also be regarded as destinations in those sentences.

Prepositions of location are often used in a figurative sense. Something abstract, without a location, is expressed as a location. A directional N-ending may also be used in these cases to express a figurative direction; for example: Mi ŝanĝos ilian malĝojon en ĝojon.

Some prepositions in themselves show direction: al, ĝis, el and de. These prepositions never show position. After these prepositions don't use the N-ending: al la urbo, ĝis la fino, el la lernejo, de la komenco.

N after adverbs of location

The N ending can also be used after locational adverbs with an E-ending, and after locational table words, to show movement in the direction of a place.

N for other meanings

N-adjects and N-supplements are most frequently used to show measure, point in time, or direction, but in some cases, the part of the phrase with the N-ending indicates another role, for which a preposition would normally be used:

Theoretically, prepositions could always be replaced with an N, if it doesn't make the meaning unclear. N is used instead of je (at) especially frequently. The rule regarding clarity, however, almost always precludes the use of N instead of the prepositions de (of) and el (from, out of), which show movement away from something, because N itself is a role marker that shows movement towards something. In some cases, however, sentences like Ili eliris la buson (They exited the bus) can be encountered. In that case, the N-ending shows an object: the bus is the object of the action "eliri" (to exit). It is much clearer, and therefore preferable, to say Ili eliris el la buso. (They exited out of the bus).

Accusative and proper names

The accusative is used with fully esperantized proper names according to all of the aforementioned rules:

Non-esperantized proper names can appear without the O-ending. The N-ending is left off of these names, even if in principle, their role in the sentence requires this ending:

If the name can accept an N-ending (if it ends in a vowel), then the ending can, of course, be added. The O-ending can also be added to a foreign name. If an O-ending is used, then an N-ending must also be used, if the word's role in a sentence requires it. The name may also be preceded by a title or another expression capable of receiving an N-ending.