Learn Finnish: Opiskelijat muokkaavat hyödyttömät tölkit ja pullot kauniiksi lampuiksi. - The students modify the useless cans and bottles into beautiful lamps.

The base word is lamppu (lamp). To form the translative plural, we use the weak stem. The double pp weakens to a single p, giving the stem lampu-. Then we add the plural marker -i- followed by the translative ending -ksi, resulting in lampuiksi. This case expresses the new state or role the items are changed into.

Why does the adjective kauniiksi look like it is in the singular form, even though it describes the plural lampuiksi?

It is actually in the plural form, but for the adjective kaunis (beautiful), the singular and plural translative forms are identical! The inflectional stem is kaunii-. When you add the plural marker -i-, it completely merges with the long -ii- of the stem. Adding the ending -ksi gives kauniiksi whether it is singular or plural.

Why are tölkit ja pullot in the nominative plural rather than the partitive?

They are the direct object of the verb muokkaavat. Because the action is a completed transformation (the students finish turning them into lamps), Finnish uses a total object. For plural total objects, the nominative plural case (ending in -t) is used. If the action were ongoing or incomplete, we would use the partitive plural (tölkkejä ja pulloja).

The verb muokata has a single k in its dictionary form, so why does it have a double kk in muokkaavat?