Learn Finnish: Omena maistuu happamalta.

In Finnish, perception verbs that express how something tastes, looks, sounds, or feels require a specific case ending. For maistua (to taste), the adjective following it must take the ablative ending -lta or -ltä. So instead of just using the basic word for sour, you have to use happamalta.

The dictionary word for sour is "hapan". Why does it change to "happama-" before the ending?

Words ending in -an or -en belong to a specific word type where the stem changes before adding endings. The -n turns into -ma- (or -mä-). Additionally, the consonant p undergoes reverse consonant gradation, doubling to pp in the open stem. This makes the stem happama-, to which you add -lta.

Can I use the "-lle" ending instead, like "Omena maistuu happamalle"?

Yes, you can! With perception verbs like maistua, näyttää, and kuulostaa, you can use either the ablative (-lta/-ltä) or the allative (-lle) case. Both happamalta and happamalle are grammatically correct and mean the exact same thing, though the -lta ending is a bit more standard in written Finnish.

Why is "omena" in its basic form here instead of the partitive case?