ARTICLE
In Esperanto there is only one article – the definite article. It is written 'la' and pronounced as something between the Russian 'lya' and 'la'. In all languages (and Esperanto is no exception), definite articles denote not some abstraction, but quite specific objects already known to both the listener and the speaker. The article is usually not translated into Russian (in some cases it can be translated as 'this', 'these'). The absence of an article is equivalent to an indefinite article. For example, the word 'portreto' without an article is an unknown portrait by an unknown artist, depicting a part of an unknown homo sapiens from the crown of the head to the middle of the chest. But if we write 'la portreto', it may well be that we have before us a very famous portrait of a quite specific person. I can already hear your suggestions. Yes, it could be the 'Mona Lisa' by Leonardo da Vinci. 'La portreto estas originala' – your French friend will say when he takes you on a tour of the Louvre. But if you have a book of reproductions in your hands, you will say: 'la portreto ne estas originala' or 'la portreto estas ne originala' (negation in Esperanto is expressed by the particle 'ne').
PLURAL NUMBER
Nothing could be simpler: just add the letter 'j' to the ending of nouns or adjectives (other parts of speech do not have a plural): planedo – planedoj (planet – planets), portreto – portretoj (portrait – portraits), krokodilo – krokodoloj (crocodile – crocodiles); bela – belaj (beautiful – beautiful), bona – bonaj (good – good).
GENITIVE CASE
There is no genitive case as such in Esperanto. Its grammatical meaning (of whom? of what?) is expressed in Esperanto by the preposition 'de', for example: gramatiko de esperanto – Esperanto grammar, centro de urbo – city center, klimato de Afriko – climate of Africa.
ACCUSATIVE CASE
But the accusative case does exist. In Esperanto there are only two cases – nominative and accusative. (For those who have forgotten their school curriculum, we remind that the accusative case answers the questions 'whom? what?'. If it's easier for you to remember 'znakhidny' – we have nothing against it.)
The accusative case (or 'accusative') in Esperanto is indicated by adding the ending 'n' to words ending in 'o' or 'a' – that is, to nouns or adjectives: mi skribas leteron (I am writing a letter), mi legas libron (I am reading a book), mi kantas kanton (I am singing a song). The accusative always denotes that the action is directed at an object: mi vidas homon (I see a person). It can also be the other way around: homo vidas min (a person sees me). Word order in Esperanto is completely free – speak however you want. The main thing is not to forget the accusative. You can say: min homo vidas, vidas min homo, homo min vidas.
The accusative case is perhaps the most difficult rule in Esperanto. That is, it's not that it's difficult in itself, it's often simply forgotten to be used. Imagine a situation. You are in a company of Esperanto-speaking friends and decide to show off a bit (it happens to everyone). 'Mi havas xevalo (horse).' Your friends exchange puzzled glances, someone starts coughing into a handkerchief, barely holding back laughter. 'Oh, something's wrong here,' you think. 'Just now...' Yes, of course, you wanted to say 'I have a horse' (literally – I have a horse), but you forgot the accusative case, and now it's not clear – who has whom?
Well – it happens to everyone. You correct yourself: 'Mi havas xevalon. Mi havas grandan, bonan, simpatian, belan xevalon (note that the accusative ending is added to both nouns and adjectives). Of course, you have a big, good, nice, beautiful horse. Mi watas xevalon kaj mia xevalo watas min (you like your horse, and it likes you).
And, as always, 'for dessert' – you have homework.
Imagine that you are in a room. Tell me what you see and who sees you (don't forget the accusative case!). When you finish, add adjectives to all words. For example: Mi vidas la patron. Patron vidas min. Mi vidas bonan patron. Bonan patron vidas min. What? What 'patron'? Don't forget that stress always falls on the penultimate syllable!