Learn Finnish: Kuka unohti kartan pelastusveneeseen? - Who forgot the map in the lifeboat?

In English, we say we forgot something in a place. However, Finnish uses a different logic for verbs of leaving or remaining, such as unohtaa (to forget), jättää (to leave behind), and jäädä (to stay). These verbs require the illative case, as if the object was placed into the location and left there.

Why is the map kartan instead of its basic form kartta?

Kartan is the direct object of the sentence. Because the action of forgetting is complete and applies to the entire map, it takes the accusative case, which looks identical to the genitive case ending in -n.

How is the illative ending formed for the word pelastusveneeseen?

The word for lifeboat is a compound of pelastus (rescue) and vene (boat). Because vene is a word that ends in -e, its illative ending is always -eseen. This makes the final word pelastusveneeseen.

How do we get the past tense verb unohti from the infinitive unohtaa?