Learn Hardcore Latin: Mercator ad oppidum ambulat. - The merchant walks to the town.

Mercator is the nominative case form, which is used for the subject of the sentence. If you saw something like Mercatorem, that would be the accusative case, for a direct object. Here, the merchant is the one doing the action, so we use Mercator.

Why is ad oppidum used instead of in oppidum?

The preposition ad indicates motion towards a place, whereas in can mean into or in depending on the case that follows. With ad, you’re emphasizing approach, so ad oppidum means "to the town." If you used in oppidum, it might emphasize entering the town's interior.

What is the case of oppidum, and why?

Oppidum is in the accusative case. When a preposition like ad is used to show physical direction or motion toward a place, the noun that follows it must be in the accusative case. Hence, oppidum, not oppido.

Why does the verb ambulat end in -t?

In Latin, -t is the usual ending for the third-person singular present tense verb form (he/she/it). Since Mercator is a third-person singular subject (the merchant), the verb that agrees with it is ambulat.

Does the word order here matter in Latin?

In Latin, word endings (cases and verb conjugations) are more important than word order for indicating grammatical relationships. While the typical word order is often Subject–Object–Verb, it’s flexible. You might still see Mercator ambulat ad oppidum or Ad oppidum mercator ambulat, but the meaning remains essentially the same.