The accusative in full: the four jobs of -n

Add -n to the direct object: mi vidas la homon, I see the person. The subject never takes it. This is the one piece of Esperanto grammar an English speaker has no instinct for, because English kept the marking on only a handful of pronouns (me, him, her, us, them, whom) and gave up on nouns entirely. The test is mechanical: ask what is being verbed.

Everything describing the object gets marked too, with the plural -j first and the -n after it: la bonajn homojn, the good people as an object. It looks like a lot of endings and it is really one decision made twice. What it buys is that an adjective can sit half a sentence away from its noun and still be unambiguous.

The same ending switches position into direction. Mi estas en la domo is I am in the house; mi iras en la domon is I go into the house. English has in and into, on and onto, then runs out of pairs and falls back on phrases like to underneath the table. Esperanto handles every preposition the same way with one ending.