Learn Hardcore Esperanto: La urbo estas granda.

Esperanto only has a definite article (la) and no indefinite article. Native English speakers often expect an equivalent to "a," but in Esperanto, you either use la for something specific or no article if it's indefinite.

What part of speech is "estas," and why does the sentence use it?

Estas is the present tense of the verb esti (to be). In this sentence, it links the subject (la urbo) with its description (granda).

Why does "urbo" end with -o, but "granda" ends with -a?

Nouns in Esperanto typically end with -o, while adjectives end with -a. Here, la urbo (the city) is a noun, and granda (big) is an adjective describing it.

Can I change the word order in this sentence without altering its meaning?

Yes. Esperanto’s flexible word order would allow something like Granda estas la urbo, although La urbo estas granda is the most straightforward, common order.

Is there any special rule about plural or accusative forms in this sentence?

No. Since urbo (city) is singular and not an object of the sentence, it remains urbo without extra endings. If it were plural, you’d add -j (e.g., la urboj), and if it were a direct object, you’d add -n (though with “to be,” there’s usually no object).